VOLUME TEN. NUMBER THREE, AUGUST 1978 PRICE: $1.50
THE AUSTRALIAN COMPUTER JOURNAL
PUBLISHED FOR THE AUSTRALIAN COMPUTER SOCIETY Registered for Posting as a publication — Category B The DEC WS78/WD78 News Briefs from the Computer World “News Briefs from the Computer World” is a regular feature which covers local and overseas developments in the computer industry including new products, interesting techniques, newsworthy projects and other topical events of interest.
DIGITAL AUSTRALIA ENTERS WORD PROCESSING culmination of the company’s achievements at that time in MARKET minicomputer and text editing technology. It offered a Digital Equipment Australia signalled its entry into combination of data processing and ready-to-use, fully the rapidly growing word-processing market in Australia dynamic text editing capabilities in a desk-sized, and New Zealand with its release recently of several diskette-based, video display workstation. computer-based word-processing systems. Then, as now, DEC’s philosophy was to introduce new products based on field-proven hardware and software, in a manner that could bring the user immediate benefit but pose little financial risk. The Datasystem 310W was followed by the lower-cost Word Station 100, offered for users without data-processing requirements. Then the Word Processing Computer Systems Group brought out the Word Station 102, a two-terminal system where second station access if could be switched among as many as six video .terminals. Here again, the objective was to increase word-processing access and volume while previous systems, output was provided by a 45-character-per-second, letter-quality printer and an optional communications package enabled transfer of information between systems. The introduction of the DX/RSTS software link, plus the announcement of the software package WPS-11M, the WT78, and WS78 products, made possible the configuration of extensive word-processing networks, with central facilities for information storage and output. At the same time, the concept and advantages of low-cost, locally The DEC W3202/WD202 controlled, stand-alone systems were retained. These products maintain the directions of DEC’s . They are the single user stand-alone Word Station 78 word-processing development and the company’s principles (WS78) which becomes the WD78 when used for word and . of product design — first, that system permit expansion in data processing, and the stand-alone Word Station 202 gradual, incremental fashion, allowing the user to keep pace (WS202) a two terminal word-processing system, based on a with his word-processing requirements and to approach his much faster processor, which becomes the WD202 when goals in progressive, manageable steps; and second, that used for word and data processing. These systems are each new product retains maximum compatibility with its expandable and, with additional options, can communicate predecessors, thereby protecting the customer’s investment with each other and other DEC computers. in installed equipment and assuring its continued Their release in Australia reflects the commitment of usefulness. Following this precept, all of DEC’s the U.S. parent company, Digital Equipment Corporation, word-processing systems from the DS310W to the WD202 to the word-processing market. In fact, DEC believes that can be mixed, matched or even used interchangeably, the future market will move beyond word processing to without retraining of operators or expensive recoding of total information processing, and the release of the hybrid software. WD78, is indicative of this belief. While DEC actively entered the computerised DATA GENERAL CORPORATION DELIVERS*50,000th word-processing market approximately two and a half years SYSTEM ago, that entry' was based on concepts and experience Data General Corporation has delivered its 50,000th dating back more than 10 years. During the early 1960s computer system, an ECLIPSE C/330. DEC initiated interactive processing on small computers, The customer, TRW Communications Systems and and that innovation is now one of the guiding principles of Services, of Los Angeles, which took delivery earlier this modern computing as well as the essence of advance word month, will use the ECLIPSE C/330 to develop new processing. products for the distributed data markets. During this earlier period the company became a The system will support a software development staff pioneer in automated typesetting systems for newspapers of more than 90 programmers, geographically distributed and commercial publishers. These efforts brought about the between TRW’s three data centres. creation of powerful video display text entry and editing The ECLIPSE C/330 will be interfaced with six systems. ■ NOVA computers, 24 on-line terminals and will be used in The.Datasystem 310W, introduced in February 1976 conjunction with 24 additional NOVA systems for as DEC’s first word-processing product, represented a development purposes.
The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Freedom of choice Datronics offer a solution to your terminal problems.
Hazeltine V.D.U.'s CB Diablo Printers Techtran Data storage LOW-COST, HIGH-PERFORMANCE HyTerm 815/6/7/8 145K character storage om VIDEO DISPLAY UNITS Model 1620 Interactive console printing ANSI-ECMA-TI and NCR recording terminal — based on the famous Diablo formats, dual RS232c/ Current Loop inter HAZELTINE 1500 “daisy wheel” printer —with standard faces. Start with the Model 815 paper tape A low-cost terminal with a host of features RS232c/current loop interface with graphics punch/reader emulator and continue through Numeric keypad built-in at no extra charge and word processing features, Model 1610 — to the 818 featuring tape editor, file skip and • Upper/lower case • Cursor read and receive only version available. string search capability. address,line insert/delete, switch-reversible HyType II “daisy wheel” Porta 200 Hand held rechargeable data video • Full 24 x 80 display on a 12-inch 3 basic printer units available with industry capture device featuring 10 hour field screen • High-legibility 7 x 10 dot matrix compatible intelligent parallel or serial operation, with keyboard and display of • Eight Switch-selectable transmission rates interfaces to speed throughput of typewriter numeric and special characters. to 19,200 baud • Horizontal tabs • Pro quality text. 950/951 Microdisc 200K storage mini grammable brightness levels • Clear to “End floppy features dual RS232c/ current loop of Line” and “End of Screen” • Remote 1660 interfaces. Model 951 gives the user Keyboard lock • Automatic repeat on all Interactive 200 CPS printing terminal — based on Diablo 9 wire dot matrix printer — powerful editing and search capability at keys • Audible alarm • Auxiliary serial very affordable prices. output port • Non-glare display • Clear high features highest throughput plus 9 optional intensity • Current Loop/RS232c. type fonts including A.P.L. 2300 1510 All the features of the standard 1500 Basic Dot Matrix printer — 200 CPS print, plus: Format mode • Cursor control keys ultra high speed tabs —bidirectional • Protected fields. printing with a complete range of interfaces. 1520 Combines the features of 1500/1510 and adds an independent intelligent printer -Jbchtk*~ controller of 2K character capacity—with dual RS232c/ or parallel output. 8©
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DC6834 ii The Australian Computer Journal, Vol. 10, No. 3, August, 1978 An unbeatable combination for digital applications. Digital delay for pulse train analysis with the PM 3261. Four channels for signal comparison with the PM 3244. a thorax a |0t more to find out from ial Equipment. FOUR 50 MHz CHANNELS ___ in compact 9.6 kg construction
DIGITALLY DELAYED TIMEBASE on compact 120 MHz oscilloscope
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/Four oo ...... channels plus two riifiererV.iais can toe ciispiayec at tne same time on mis new comoact /Philips oscilloscope PM 3244. The instrument also / features fully independent triggering ot mam and / delayed time bases. The main timebase can be triggered on any of the four channels plus composite, external and Fast and accurate location of individual events in data line.The delayed timebase can also be triggered on any streams of up to 100,000 bits is provided by this new 1 of the four channels plus composite. These facilities Philips oscilloscope PM 3261. In addition to conventional give many display possibilities, allowing, for example, a triggering facilities, the instrument features a digitally ofgivemagnified the many sou, detail displayv.,.— . of apossibilities. delayed event o„v to.... be„ displayed eve,even delayed timebase that can be set to trigger on a particu when>Mhe»n it is not directly related to the main timebase lar pulse in the stream, the position being displayed on a triggering reference.-~ ThThe° PM 3244 also features a Ilarge built-in five-digit LED. In order to select the position of the 8 x 10 cm screen and a compact, 9.6~ ~ kg "^nstruconstruction. event, the delay counter can be set to count up or down at an adjustable speed, which can be as low as one step Despite the apparent complexity of the many display every two seconds. This allows specific sections of the Easymodes, to usethe instrument is extremely easy to use. Controls data stream to be examined and the counting stopped are logically grouped and positioned to fall naturally to and stepped back in order to pick up and locate any irre hand. This is made possible by the extensive use of cold gularities. The digitally delayed counter also overcomes switching techniques, which remove the mechanical problems qf jitter, such as occur in mechanical systems connections between the front panel and the PC like disc memories, tape drives, etc. In such cases, if the boards. Instead, the switching is performed on the boards, jitter is longer than one period, a conventional delayed with simple DC signals from the controls. The controls timebase cannot be effectively employed. A further digi can therefore be positioned anywhere on the front pane! tal facility is the TTl output pulse at the rear of the and the PC boards designed for optimum layouts at all instrument, which can be used to reset the circuitry signal speeds. The PM 3244 also features a remarkably without waiting for the end of the pulse train. low 29 W power consumption that eliminates the need Conventional operation with trouble-free triggering for ventilation holes and fans. This boosts reliability and Once the display has been 'trapped' using the digitally allows the instrument to operate for long periods from a delayed timebase, accurate time interval measurements hancrv pack, as well as just about any voltage/ can be made using the normal delayed timebase QHOWb - vveu controls. In addition the main timebase has a TTL frequency combination. triggering facility, which completely eliminates prob lems of triggering on preshoot, overshoot, ringing, etc., since the signal must pass a defined trigger window of + 0.8.., 2.0 V DC. For further information write to Philips Scientific & Industrial Equipment, P.O. Box 119, North Ryde. N.S.W. 2113 or phone Sydney 8888222 Melbourne699 0300
Test and Measuring PHILIPS PHILIPS Instruments 132-0015
Vol. 10, No. 3, August, 1978 The Australian Computer Journal, CSA Computer Sciences of Australia Pty. Ltd.
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COMPUTER SCIENCES OF AUSTRALIA CSA Centre, 460 Pacific Highway, St. Leonards. N.S.W. 2065. Telephone: 439-0033
SYDNEY: MELBOURNE: BRISBANE: NASHUA HOUSE, 33 ALBERT ROAD, 87 WICKHAM TERRACE, 34 CHANDOS ST„ ST. LEONARDS MELBOURNE, VIC. 3004 BRISBANE, OLD. 4000 N.S.W. 2065 (03) 267-2533 (07) 229-3966 (02) 439-5444
ADELAIDE: PERTH: CANBERRA: 12-14 GLEN OSMOND ROAD, 16 STIRLING HIGHWAY, 88 NORTHBOURNE AVENUE, PARKSIDE, S.A. 5063 NEDLANDS, W.A. 6009 BRADDON, A.C.T. 2601 (08) 272-6788 (09) 386-8266 (062) 47 8611 SENIOR CSA STAFF AT TECHNICAL CONFERENCE The CS/60 can be the sole business computer for More than 40 senior staff of Computer Sciences of firms in the $5-$25 million sales range or handle the data Australia Pty. Limited participated in the company’s processing needs of one department in a major corporation. two-day technical conference, held in Sydney in June. As many as 12 people from different work stations can CSA’s General Manager, Mr. Robert Kassel, said the operate the computer at one time. conference was arranged as a forum for the exchange of technical information among CSA professionals. U.S. BUSINESS FORMS EXPERT FOR ACS-8 “We operate in a high-technology environment and An American expert in the total management of seek to give our senior staff opportunities each year to business forms, Mr. Jack Stubbs of Moore Business Forms share information gained in the practical application of this Inc, has been invited to visit Australia to speak at the technology on behalf of our customers,” Mr. Kassel said. ACS-8 Computer Conference in Canberra this month. Professor J.M. Bennett, Professor of Physics (Electronic His visit coincides with a major effort by the Computing) was a guest speaker at the conference. Australian sister company, Moore Paragon Australia Eight papers were selected for presentation at the Limited to help launch the “Forms Management conference. The papers covered: Programme” concept to Australian companies. * Requirements for the technical planning and Moore Paragon has found that the cost of supplying control of large-scale data processing projects. forms is minute compared to the cost of using them — * Techniques for the conversion of large supply is a mere one to five per cent of the “real” cost. production application programs to a new host The Forms Management Programme concept looks at computer. the areas of greatest savings - through proper forms design, * Use of structured design and programming systems design, and better overall forms management. techniques for life cycle support of a complex Mr. Stubbs has an understanding of business forms system. management from both the client and manufacturing * Criteria for the selection of design approaches viewpoints. to data networks. He was a foundation member of the Data Processing * Integration of mini-computers into a large-scale Managers Association in North America. distributed data processing system. While working as a data processing manager for * Decision criteria for the selection and use of Moore in Toronto, Canada, he was involved in the public or shared tele-processing systems. formation and development of the Toronto chapter of the * Decision criteria for the selection of a particular DPMA, and later played an active part in the Montreal class of data base management system to meet Chapter from 1959 onwards. given operational requirements. Now a member of the Marketing Division of Moore * Criteria for the selection of data processing Business Forms Inc, Illinois, USA, Mr. Stubbs continues his equipment for given operational use. interest in DPMA affairs. The conference was a highlight in a year in which DR. JAMES CUNNINGHAM HEADS NATIONAL other major developments were the completion of CSA’s SEMICONDUCTOR'S NEW MAGNETIC BUBBLE national INFONET network with the opening of a branch MEMORY OPERATION office in Perth; the amalgamation of the company’s A new business activity which will develop and Contract Services and Facilities Management Divisions in a market computer microcircuit products based on the new operating unit, System Services Division; and the magnetic bubble domain technology has been established formation of a Professional Services group within the by National Semiconductor, with Dr. James Cunningham in Network Services Division. charge. Dr. Cunningham, who was most recently with Intersil Corporation as senior vice-president and manager of DATA GENERAL EXPANDS BUSINESS COMPUTER the digital products division, reports to Pierre Lamond, LINE National’s vice-president and director of technology. A major expansion of its business computer line with “Magnetic bubble technology has only recently the introduction of two new series has been announced by emerged as a reliable and economical means of producing Data General Australia Pty. Ltd. computer memory components capable of storing a large The CS/20 is a desk-top unit designed for businesses quantity of data bits,” Dr. Cunningham said. “The most with as few as four employees and revenues of $500,000 to promising potential use for bubble memories is in the $1,000,000. The CS/60 is Data General’s largest small replacement of mechanical memories such as magnetic disc business computer. and tape equipment.” Mr. David Taylor, the company’s National Sales According to Dr. Cunningham, the potential market Manager, said: “The CS/20 significantly broadens the for such low cost, large memory storage units is enormous. market for small business computers because of its low By the end of this decade, the domestic market for rotating price and ease of use. The new CS/20 and CS/60 combined memory systems and solid state memory components with the previously announced CS/40 comprise one of the should reach $5 billion annually, he estimates, with about widest ranges of small business computers in the industry.” $50 million of that spent yearly on magnetic bubble type The CS/20 is the only small business computer memory devices. programmed in an “interactive” version of standard Although slower than the latest bipolar and MOS COBOL, the most popular business language. random access memories (RAMS), the magnetic bubble Secretaries and clerical personnel can be easily taught devices are attractive replacements for many types of to operate the computer in conversational dialogue. rotating magnetic memories because they are non-volatile; Another advantage of the system is that it runs on i.e., in the event of electrical power failure the stored data standard electrical current in an office environment. would not be lost. They are also believed to be much more
The Australian Computer Journal, Vol. 10, No. 3, August, 1978 V reliable than the various forms of rotating memory. proved to be extremely popular, being reliable, high-quality According to Dr. Cunningham, National and competitively priced. The keyboard printer terminals Semiconductor, one of the major manufacturers of memory are available ex stock for under $1300 in one-off quantities. components, will be introducing its first bubble memories The 43 range is rapidly expanding into a variety of during 1980. “Bubble memories involve disciplines that are configurations. new to the semiconductor industry,” he noted, “because STC has recently announced the addition of new while bubbles do involve some of the same production eight-level model 43 Buffered terminals which will techniques, bubbles aren’t actually semiconductors.” incorporate up to 20,000-character solid state storage for A typical bubble memory might contain between sending and receiving and editing, with on-line speeds from 100,000 and 250,000 memory bits organized in a serial 10-180 cps. These terminals can receive data from line path device. Instead of silicon or another semiconductor whilst data is being prepared by the operator. ASR models material, the bubble memory is constructed on a thin including paper tape are also being added to the range and magnetic garnet film. Microscopic domains of magnetic will be available in both ASCII and telex versions. polarization, commonly referred to as bubbles, are moved With the advent of mini-computers STC has been by means of a moving magnetic field with its lines of force intimately concerned with mini-computer systems including parallel to the plane of the film. The presence or absence of a large range of peripheral devices and terminals in addition the bubbles is used to designate binary information, and the to Teletype products. domains can be added or removed by means of Expertise gained in installing and maintaining this electromagnetic loops along the surface of the film. large range of equipment on an Australia wide basis has Further information is available from N.S. enabled STC to successfully undertake third party Electronics, Bayswater, Melbourne, Vic. maintenance and now provides this type of service to a number of vendors and end-users of computer systems and STC TO EXHIBIT AT ACS-8 terminals. STC will be exhibiting some of the latest Teletype Corporation products including the model 40 and 43 range DIGITAL INTRODUCES ADVANCED INTERACTIVE at the ACS-8 Exhibition in Canberra later this month. Of TRANSACTION SYSTEM particular interest are the model 40 printer for OEM’s Digital Equipment has introduced the industry’s most which is a high performance (3001pm) heavy-duty line comprehensive minicomputer-based system for interactive printer available in the price range $2200-$3300; and the transaction processing. new model 43s. Named TRAX, this is the first system specifically The Teletype model 43, introduced in 1977, has (Continued on page ix at back) TELERAY CRT'S 3741 3541 Asychronous Communication Character Mode Edit Upper/Lower Case Displayed Space over Data 110-9600 Baud Dual Baud Switch 24 x 80 Character Display 110-9600 Baud Numeric Key Pad (Opt) Parallel Printer Out (Opt) 128 Characters Generated Upper Case Display RS 232 and 20MA Current Wide Character Switch Loop Interfaces Standard Video Output (Opt) Printer Output (Opt) RS 232 and Current Loop i '. \ ' \Y\ 11' v ;' i' \ \ *' a 3841/XY Interfaces Standard WmsS XY Cursor Addressable 3931/APL As per 3711 but Cursor APL Pairing Keyboard Addressable APL Overstrike Character Mode Edit Teleray 3541 110-9600 Baud a5P ANDERSON DIGITAL EQUIPMENTS PO BOX 322, MT WAVERLEY, VICTORIA 543 2077 SEE US ON STAND 21 PO BOX 294, RYDE, NSW 808 1444 AT ACS-8 BRSIBANE 59 6436, PERTH 325 5722, CANBERRA 58 1811, ADELAIDE 79 9211, HOBART IN CANBERRA 34 4522, DARWIN 8 12505, AUCKLAND 87 6570, WELLINGTON 64 4585. vi The Australian Computer Journal, Vol. 10, No. 3, August, 1978 THE AUSTRALIAN COMPUTER JOURNAL Price: $3.50 per copy to non-members. $1.50 per copy to members. Volume 10, Number 3 AUGUST, 1978
The Australian Computer Journal is an official publication of the Australian Computer Society Incorporated. Contents: Subscription and orders should be sent to PO Box 640, Crows Next, 2065. Office-Bearers 82-86 Software Physics and Program Analysis President: A.R. BENSON D.J.J. van der KNIJFF Vice-President: A.H.J. SALE Immediate Past President: R.S. NORTHCOTE 87-97 Is Disciplined Programming Transferable, National Treasurer: V.G. WHITELEY and is it Insightful? National Secretary: G.K. PIRIE CHARLES LAKOS and ARTHUR SALE Chief Executive Officer: R.W. RUTLEDGE P.O. Box 640, CROWS NEXT, N.S.W. 2065 98-101 Part Management in the CYBER76-CSIRONET Telephone: 929.2219 Interface Editorial Committee: B.J. AUSTIN Editor: A.Y. MONTGOMERY Department of Computer Science, 102-114 A SNOBOL 4 Program to Clean Up Monash University, Clayton, Victoria. 3168 FOR TRAN Source Associate Editors: JOHN D. BLACKBURN J.M. BENNETT, G.N. LANCE, 115-117 A Criterion for Determining the Number T. PEARCEY, of Groups in a Classification P.C. POOLE D.A. RATKOWSKY and G.N. LANCE Published by: Associated Business Publications, 28 Chippen Street, Chippendale, N.S.W. 2008. Tel. 699-5601, 699-1154. Represented by: Queensland: Beale Media Services, 232 St. Paul’s Terrace, Fortitude Valley, Brisbane. Phone 52-5827. Special Features: Victoria and South Australia: Derrick, Lewis & Associates, Ashley House, 409 St Kilda Road, Melbourne 3004. Phone 2674022. U.S.A.: International Newspaper and 86,114 Book Reviews Trade Advertising, 1560 Broadway, New York, 36. 101 An Overview of Programming Practices Italy: Publicitas, Via E. Filiberto 4, - Appendix A, Appendix B Milan. France: Gustav Elm, 41 Avenue J.M. YOHE Montaigne, Paris 8. Advertising inquiries should be referred 118-119 Letters to the Editor to one of the above addresses. Printed by: 119 Forthcoming National and International Events Publicity Press Ltd., 29-31 Meagher Street, Chippendale, N.S.W. 2008.
SUBSCRIPTIONS: The annual subscription is $10.00. All REPRINTS: 50 copies of reprints will be provided to authors. subscriptions to the Journal are payable in advance and should be Additional reprints can be obtained, according to the scale of sent (in Australian currency) to the Australian Computer Society charges supplied by the publishers with proofs. Reprints of Inc., P.O. Box 640, Crows Nest, N.S.W. 2065. individual papers may be purchased for 50 cents each from the Printers (Publicity Press). PRICE TO NON-MEMBERS: There are now 4 issues per annum. The price of individual copies of back issues still available is $1.50. PAPERS: Papers should be submitted to the Editor, authors should Some are already out of print. Issues for the current year are consult the notes published in Volume 9, pp. 45-49 (or request a available at $3.50 per copy. All of these may be obtained from the copy from the National Secretariat). National Secretariat, P.O. Box 640, Crows Nest, N.S.W. 2065. No trade discounts are given, and agents should recover their own MEMBERSHIP: Membership of the Society is via a Branch. handling charges. Special rates apply to members of other Computer Branches are autonomous in local matters, and may charge different Societies and applications should be made to the Society concerned. membership subscriptions. Information may be obtained from the following Branch Honorary Secretaries. Canberra: P.O. Box 446, MEMBERS: The current issue of the Journal is supplied to personal Canberra City, A.C.T. 2601. N.S.W.: P.O. Box N250, Grosvenor St, members and to Corresponding Institutions. A member joining Sydney, N.S.W. 2000. Qld: Box 1484, G.P.O., Brisbane, Qld. 4001. part-way through a calendar year is entitled to receive one copy of S.A.: Box 2423, G.P.O., Adelaide, S.A. 5001. W.A.: Box F320, each issue of the Journal published earlier in that calendar year. G.P.O. Perth, W.A. 6001. Vic.: P.O. Box 98, East Melbourne, Vic. Back numbers are supplied to members while supplies last, for a 3002. Tas.: P.O. Box 216, Sandy Bay, Tas. 7005. charge of $1.50 per copy. To ensure receipt of all issues, members should advise the Branch Honorary Secretary concerned, or the National Secretariat, promptly of any change of address. Copyright ©1978. Australian Computer Society Inc. The Australian Computer Journal, Vol. 10, No. 3, August, 1978 81 Software Physics and Program Analysis
By D.J.J. van der Knijff*
Software Physics is a term used to describe the analysis of programs to extract software engineering measures from particular general properties of the programs. It may be used to compare programs and languages, and to improve estimation procedures in the software industry. This paper introduces the reader to the terms used in Software Physics and its application to some problems. A selection of recent empirical analyses are presented to enable the reader to make comparisons with other methods. KEYWORDS: Measurement of algorithms, programming languages, algorithm implementation, Software Physics. CR CATEGORIES: 4.6,5.2. 1. INTRODUCTION expected error rate (6.1), ideal module size (6.2), and Software Physics is an experimental science which implementation time (6.3) for an algorithm. Some as yet deals unresolved difficulties are looked at in section 7. “only with those properties of algorithms that can be As well as practical measures, research has been done measured, either directly or indirectly, statically or on modelling the algorithm writing process. A number of dynamically, and with relationships among these simple models have been developed which give close properties that remain invariant under translation agreements with the basic measures (8.1). Further study of from one language to another” (Halstead 1977b). these models has shown that the frequency distributions for This paper reviews some of the more recent empirical operators and operands within an algorithm can be closely analyses of programs and then introduces the field of simulated by relations for frequency distributions of Software Physics, along with its application to some current syntactic units in natural languages (8.2). problems. The analysis of programs, either to measure the 2. EMPIRICAL MEASURES effects of such things as changes in programming method Early measures of software were mainly ad hoc with ology or the use of different languages, or as empirical data little justification. The measures used were those that were on which to base future predictions, has assumed more readily available (e.g. number of statements, lines of code, importance in recent years due to the increasing cost of etc.), or were felt intuitively to be relevant (e.g. number of software. goto’s, subroutines, etc.), and were easily measurable. Traditionally such analysis of programs has been done Problems arose, however, when different results were on an empirical basis, however the results have generally compared, due to different definitions used. It has recently been confined to single languages and particular been shown (Johnson 1977) how different definitions of programming environments. Some examples of such lines-of-code and man-days could lead to differences by analyses are given in section 2. In recent years a new field, factors of up to 120 in measures of productivity (output/ Software Physics, has evolved, which attempts to measure unit time). programs in a language independent way. The basis for this There have, however, been a number of very good field was established by Halstead (1972) when he analyses. In particular there is the work of Elshoff, who formulated the basic measures of an algorithm. Useful studied a set of production PL/1 programs (Elshoff 1976a) results have been produced in areas such as expected error to produce a numerical profile of such a program. This rates, ideal module size, and estimated time to write profile included statement type distribution, operator programs. distribution, number of operators per expression, number In succeeding sections definitions are given for the of statements between uses of the same identifier, etc. length (sections 3.1, 3.2), vocabulary (3.1), and volume The measures indicated that most programmers had a poor (3.3) for any algorithm. From the problem statement the command of the language and that control flow through minimum or potential volume (3.3) can be determined, and the programs was extremely difficult to comprehend. Only hence the level (3.4) of the algorithm (the ratio of its 17% of IF statements had an ELSE clause, whereas hand potential volume to its actual volume). From these analysis showed that between 50% and 80% of IF state measures two further experimentally validated measures ments had had GOTO constructions used to achieve the have been derived, the effort (4.) required to implement an effect of an ELSE. algorithm and the language level (5.) of the langailge in In a later study (Elshoff 1977), of programs which it was written. These measures are the most developed at some of the same installations after powerful, since from them it is possible to estimate “structured programming” techniques had been adopted, a number of differences were apparent. The usage of GOTO’s “Copyright © 1978, Australian Computer Society Inc. had decreased (from 11.7% to 2.8% of the total number General permission to republish, but not for profit, all or part of this material is granted, provided that ACJ’s copyright notice is of statements), while there was marked increases in the given and that reference is made to the publication, to its date of use of PROCEDURE statements (from 0.2% to 1.7% of issue, and to the fact that reprinting privileges were granted by total statements), IF statements containing ELSE clauses permission of the Australian Computer Society.” (from 17% to 36% of number of IF statements) and DO
*Department of Computer Science, Melbourne University, Parkville, 3052. Manuscript received 31st January, 1978. Revised Manuscript Received 13th June, 1978.
82 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Software Physics statements with WHILE conditions (from 0.1% to 5.6% N5»n1log2n1 +n2log2n2 (1) of DO statements). Observed changes in control structure This relation is probably the most fundamental relation of and programming style indicated that actions were now Software Physics. It has been extensively tested by a being performed at the point where the decision was number of researchers. In particular Elshoff (1976b) has made, whereas previously decisions had been nested with tested and confirmed the relation for a large sample taken branches to where the action was performed. These changes from a production environment, rather than published improved readability and understanding of the programs, algorithms which had formed the data for earlier tests. A and hence helped reduce maintenance effort. theoretical justification for this result has been presented Robinson and Torson (1976) have done a similar by Halstead (1977b). analysis of FORTRAN programs with a view to optimising Although little can be directly inferred from the compiler design towards actual usage. Their analysis has length (N) we shall show in later sections that a number of shown that most programs contain mainly simple results can be expressed in terms of N and can thus be constructs, hence compilers could be made more efficient related approximately to number of program statements, by checking simple things first (e.g. tests for variable = since for most languages an approximate conversion is constant or variable = variable, before testing for a more possible, given the average number of operators and complex assignment, would succeed in 42% of cases). operands per statement. A simpler analysis by Hall and Kidman (1975) has produced a measure of “structuredness” (based on upward 3.3 Volume and Potential Volume branches and DO loops) which has been used for assessing From the length and vocabulary we can find the simple student jobs. theoretical volume (V) of the algorithm. This is given by These measures are language dependent however, and the length times the number of bits required for a unique as the depth of study increases become more so (the pointer to each item in the vocabulary number of times the “while” construct is used in a PL/1 i.e. V = Nlog2n (2) program has little relevance to FORTRAN). As Sammet We can also define the minimum or potential volume (1972) has shown, in her report on language comparison, (V*) for an algorithm. This is obtained if the algorithm it is possible to partly avoid this language dependence. already exists in the language as a callable procedure. We While indicating the possibility of absolute measures she need then only calculate the volume of the procedure call. did not see them as feasible then, and so gave a method This has two operators (the procedure name and a grouping whereby small groups of languages could be compared symbol) and a number of operands (n2) equal to the relative to each other. number of conceptually unique input/output parameters In order to obtain more general results, i.e. results (including constants). Since each item in the vocabulary is which are applicable over a large range of programs and used only once, the length equals the vocabulary and languages, we need language independent measures. Such V* = (2+n*)log2(2 + n*) (3) measures form the basis of Software Physics. 3.4 The Level of an Algorithm 3. THE MEASURES OF SOFTWARE PHYSICS Given the above definitions, we can define the level Software Physics is based on operators and operands. (L) of an algorithm as the ratio of its potential volume to Halstead (1977b) has defined an operand as a variable or its actual volume constant, and an operator as a symbol or combination of i.e. L = V*/V (4) symbols that affects the value of ordering of an operand. Thus, for a given problem, in an ideal language (where the An algorithm is then defined as consisting solely of algorithm is available as a callable procedure) the level will operators and operands. Thus IF, WHILE etc. are be 1, however if we change the language so that the volume operators while BEGIN . . END is considered as a single is increased (i.e. we must explicitly code the algorithm) grouping operator. Declarations are not considered as being then the level will fall below 1. part of the algorithm. Halstead has shown (1977b) that level can be approximated by 3.1 The Basic Measures Halstead has defined (1972) four basic measures for any algorithm. nx — count of distinct operators Although this approximation gives good results in simple n2 — count of distinct operands cases it has since been shown (Oldehoeft 1977) that in ill- Nj — count of operator usages conditioned examples the values produced by the two N2 — count of operand usages measures can be widely disparate, hence he recommends Given that the vocabulary of an algorithm consists of the use of the former wherever possible. the set of operators and operands, the size of the vocabu- lare is then defined as 3.5 Program Purity n = nj + n2 As we noted earlier correlations can be shown (Halstead refers to the value ‘n’ as the vocabulary), and the between measurable program attributes and the presence length of the algorithm is defined as of poor programming practices. We may define (Halstead N = N, +N2 1977c) six classes of “impurities” in a program. These are:— 3.2 The Length Equation I Complementary operations — the successive In his first study Halstead (1972) discovered that the application of two complementary operators to the length (N) of well written programs, was related to the same operand e.g. A + B — B. vocabulary by II Ambiguous operands — the use of a given operand to The Australian Computer Journal, Vol. 10, No. 3, August, 1978 83 Software Physics refer to different things at different times e.g. A: = 5. LANGUAGE LEVEL A + A. As a final measure Halstead (1973) has defined the III Synonymous operands — the complement of ambigu level of a language. As was noted earlier if the language is ous, where two names refer to the same thing. varied while holding the problem constant the level (L) of IV Common subexpressions — when the same operation the algorithm varies inversely with the volume (V). A is repeated, rather than a new name being assigned. similar relation has been observed if the language is held V Unwarranted assignment — when an unnecessary constant and the problem (hence V*) is varied, whereby L operand is introduced. varies inversely with V*. Language level (X) is thus defined VI Unfactored expressions. by These impurities show up in a number of ways. X = LV* (=L2V from equation (4)) (7) Halstead (1977b) developed a procedure to try and detect The hypothesis that X is constant for a particular program impurities which involved calculating L (using language has been tested over a wide range of languages and equation (5)) and V (from equation (2)) and comparing the problems. By rewriting the equation as X = LbV and then product (LV) with the value for V* computed from solving for b, Halstead (1977b) has produced a value of equation (3). The presence of impurities of types I, II and b = 1.987, however no measure of dispersion is given, IV causes the product LV to be less than V*, while types although he states that the variance is quite large. III, V and VI cause it to be greater. This implies that Values for X have been calculated by Halstead for agreement between LV and V* does not guarantee lack of various languages. He found that the values tend to lie impurities, but a sizeable discrepancy may be taken as near 1 (X = 1.53 for PL/1, 1.14 for FORTRAN, .88 for evidence of the presence of one or more impurities. COMPASS etc), and when the languages are ranked based upon the value of X, there appears to be considerable 4. THE EFFORT HYPOTHESIS conformity with intuitive ideas concerning the relative Based on the measures and relationships of the power of various programming languages. previous section Funami and Halstead (1977) have The values given are mean values, in the samples produced a hypothesis whereby the effort (E) involved in sizeable variances occurred in values of X which have not writing an algorithm may be measured. The expression for been completely resolved, and estimates based on X must E may be regarded as somewhat counter-intuitive, and since be regarded as approximate. it forms an important part of many practical results, its derivation will be given here in its entirety. The following 6. APPLICATIONS OF THE MEASURES steps are used to yield a value for E in terms of elementary The values for effort (E) and language level (X) have mental discriminations (the smallest distinguishable mental been shown to have a number of uses in explaining certain action). observations and allowing predictions to be made. 1. A program must consist of N non-random selections from the n items in the vocabulary. 6.1 Error Rates 2. Each selection involves a search among the n items. While the measures do not allow us to detect the 3. Assume this search can be approximated by a binary presence of errors they do enable us to predict the like search. lihood of errors. Bell and Sullivan (1974) have done a 4. Each binary search will require log2n comparisons. study on those algorithms published, and subsequently 5. Therefore a program is generated by making Nlog2n certified, in the series printed in Communications of the comparison. Association for Computing Machinery. They calculated 6. Since volume (V) = Nlog2n, the volume is therefore the length, N, of these programs, and found that no correct a count of the number of comparisons required to program had N > 237, and that only one incorrect program generate a program. had N < 284. They thus recommended that no algorithm 7. Assume that the number of elementary mental with N > 260 should be published without special discriminations per comparison is a measure of the certification. Using the value of E, as obtained from the difficulty of the task. effort equation, as an indicator of the number of 8. Assume that the level (L) is the reciprocal of the opportunities for error, Halstead (1977) has deduced the difficulty. “Mean number of elementary mental discriminations 9. Then E, the count of elementary mental discrimina between potential errors in programming”. This value tions is given by (ECrit) has been found to have a value of 3000, and the E = V/L (6) predicted number of bugs, B, is to be found by This hypothesis has been extensively tested.' Using B = V/3000 data given by Akiyama (1971) in a paper correlating the or B = E2/3/3000 number of bugs to a simple measure of complexity, since V =E2/3/xt/3 Funami and Halstead have deduced the basic measures andX1/3 ^ 1 given previously, and hence E, and have shown a corre hence the volume of a program likely to have no bugs can lation between E and the number of bugs of .98. be found by setting B = 0.5, which gives V = 1500 and N = Drawing on work by Stroud (1966) in measuring 260. The exact correspondence of this measure with Bell psychological time, Halstead (1977a) has shown that an and Sullivan’s findings is coincidental, but it does give a independent measure of E obtained by multiplying justifiable measure for maximum module size in large implementation time by the Stroud number (the number programs. of elementary mental discriminations per second) gives a good correlation with E as calculated above for programs 6.2 Ideal Module Size whose implementation time ranges from 5 minutes to Halstead (1977b) has shown that it is possible to 1000 man-years. Further discussion of these results will be obtain values for n and N from X and n2. From Bell and postponed until after the section on language level. Sullivans figures for tire average size of a correct program 84 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Software Physics
(N = 162) and using figures obtained from equations composed of n entities (the vocabulary), and that the optimizing modular length (N) and potential volume (V*), algorithm is generated by randomly choosing one of n until he has further shown that the number of modules (M) in each has been chosen at least once. an algorithm should be given by Model B — This recognises the difference between M = n*/6 operators and operands, and assumes that they alternate, thus the algorithm is generated by picking one of n2 then 6.3 Programming Time picking randomly alternately from nj and n2 until each Having found how many “error-free” modules will be of nj and n2 has been chosen at least once. required in our “pure” program, we may well ask how long Model C — This is the most complex of the models, it will take to write. This value is also available, since, from and accounts for the fact that a programmer is unlikely the work of Stroud (1966) in measuring psychological time, to duplicate code, but rather to introduce temporary it has been shown that the human brain performs between variables. Model C modifies the model B selection process 5 and 20 elementary mental discriminations per second. such that operand-operator-operand triplets which have Halstead has assumed that a programmer working been selected previously are not available for selection efficiently performs approximately 18 such discriminations again. per second. He refers to this value as the Stroud number The lengths (as defined previously) for each of these (S). Thus models has been shown by Bayer to be in close agreement T = E/S with the lengths as predicted by the length equation (see This equation has been tested (qv. section 4) and 4.2). shown to give good correlation to independently published figures, although allowance would have to be made for 8.2 Physical Structure programmer variations when making predictions. Zweben (1977) has carried this work further by Since E can be determined solely from X and V* by drawing on relations from linguistics. In particular he has the following, used Zipfs Law (1949) as modified by Mandelbrot (1952) E = V/L ( equation (6)) to aid in prediction of operator and operand frequencies. L = V*/V ( equation (4)) He has shown that operator and operand frequencies need and X = LV* ( equation (7) ) to be handled differently. He shows that Zipfs Law for the hence E = V2/V* ( from equations (4) and (6)) frequency of the ith most common word (f;) and (V*)2 = XV ( from equations (4) and (7)) fi = n/i hence E = (V*)3/X2, when applied to operators gives a good fit, but gives if the problem (V*) and language (X) are known, it is discrepancies at the higher frequency end. possible to determine effort, and hence time from the Zweben then notes that Mandelbrot has observed the starting conditions. same sort of discrepancies in natural language text. Mandel brot indicated that instead of the frequency ratios 7. SOME PROBLEMS behaving like 1/i, as Zipfs law predicts, they behave like We have just seen how E can be calculated from X and (1 + m)/(i + m) for small i. By using V*. Since V* may be found from n*, E may be found from m = (ni -i)/ni X and n*. Halstead (1977b) has shown that all the basic Zweben has obtained the formula parameters may be found using only these two values. The fi = ((1 + m)/(i + m)).fj results of such predictions must be regarded simply as where guidelines to the actual values since in the experimental fni > for nj > n2 determination of the values for X for the various languages fi = sizeable variations occur, which are as yet unresolved. ln1.(n2/n1) = n2, for n2 > nj Some problems are also present in the case of that is operator definition since Halstead has argued that since fx = max(nj, n2). labels have no meaning on their own (an unreferenced label For operands he has shown that this does not hold. being simply a comment) the label part of a “goto” forms He has shown instead that the ratios of the frequencies of part of the operator (“goto label 1” is thus a separate the terms remains constant, unlike Zipfs Law, where they operator from “goto label 2”). While this has the useful behave like 1/i. Hence if we can find two frequencies from effect of making the value of nj open-ended, it poses this model we can find the rest. interesting questions when counting certain languages, such It remains only to find two. Zweben proposes that fj, as Assembler or PL/1, which would appear to have variable the frequency of the most common element, is operators. fi =(n2 - l)/log2n| and fn2, the least common element 8. THEORETICAL STUDY OF ALGORITHMS fn2 = 1 Starting from the basic parameters and relations a hence we can determine that number of experiments have been conducted in modelling program construction in order to understand why these f. = f^n2 — 0/(n2 - 1) relations hold. and further N2=fj (rn2 - l)/(r — 1) 8.1 Modelling where Bayer (1972) has developed three models of program r = (l/f1)1^n2 ~ ^ construction which have been used as a basis for further study. In order of increasing complexity these are: These relations have been tested on the first fourteen Model A — This assumes that an algorithm is algorithms from CACM. The algorithms have also been
The Australian Computer Journal, Vol. 10, No. 3, August, 1978 85 Software Physics translated into FORTRAN, PL/1 and PILOT, and the ELSHOFF, J.L., “The Influence of Structured Programming on PL/1 Program Profiles”, IEEE Trans, on Software Engin relationships have been shown still to hold, however a eering, Vol. SE-3, No. 5, Sept 1977, p364. number which were translated into COMPASS had minor FUNAMI, Y. and HALSTEAD, M.H., “A Software Physics Analysis discrepancies. This was ascribed to the distant relationship of Skiyama’s Debugging Data”, in Computer Software to natural languages, which seems to be correct, since the Engineering, J. Fox, ed., Polytechnic Press, NY 1976, pi33. HALL, H.M. and KIDMAN, B.P., “Empirical Analysis of BASIC discrepancies occurred with the EOS operator only, and the and FORTRAN Programs”, in Computers in Education, 0. relations hold elsewhere. The results are given as correlation Lecarme and R. Lewis, eds., IFIP, North-Holland, 1975, coefficients and slope of best fit with every few dispersion p313. measures. HALSTEAD, M.H., “Natural Laws Controlling Algorithm Struc ture?”, A CM SIGPLAN Notices, 7,2,Feb. 1972, p.19. HALSTEAD, M.H., “Language Level, A Missing Concept in Infor mation Theory”, ACM SIGME Performance Evaluation 9. CONCLUSION Review, Vol. 2, No. 1, March 1973, p.7. Software Physics is a new field which is expanding HALSTEAD, M.H., “An Experimental Determination of the rapidly. Halstead (1977b) has indicated that applications ‘Purity’ of a Trivial Algorithm”, ACM SIGME Performance may be made in areas not explicitly related to software Evaluation Review, Vol. 2, No. 1, March 1973, p.10. (although these have been deemed to fall outside the scope HALSTEAD, M.H., “Potential Contribution of Software Science to Software Reliability”, Dept. Comp.Sci., Purdue Univ., of this paper), and research is currently going forward in Lafayette, IN, Report CSD-TR 229, 1977. many directly related areas. The only limiting factor to HALSTEAD, M.H., “Elements of Software Science”, Elsvier North- widespread application of the measures is the unavailability Holland, NY, 1977. JOHNSON, J.R., “A Working Measure of Productivity”, Datamation of the basic counts of operators and operands. When these Vol. 23, No. 2, Feb. 1977, p.106. become accepted as standard output from compilers we can MANDELBROT, B., “Contribution a la Theorie Mathematique des look forward to the general use of the measures as a basic jeux de Communication”, Ph.D. dissertation, Paris, France, tool of analysts and programmers. Dec. 1952, Publication of I'Inst. de statistique de TUniv. de Paris, Vol. 2, fasc.1,2,1953. OLDEHOEFT, R.R., “A Contrast Between Language Level Bibliography Measures”, IEEE Trans, on Software Engineering, Vol. SE-3, AKIYAMA, F., “An example of Software System Debugging.”, No. 6, Nov. 1977, p.476. Proc. IFIP Congress, 1971, p353. ROBINSON, S.K. and TORSUN, I.S., “An Empirical Analysis of BAYER, R., “A Theoretical Study of Halstead’s Software Phenom- FORTRAN Programs”, the Computer Journal, Vol. 20, No. onen.” Dept. Comp. Sci. Purdue Univ. Lafayette, IN, Report 1, Feb. 1976, p.56. CSD-TR69, 1972. SAMMET, J., “Problems In, and a Pragmatic Approach to, Pro BELL, D.E. and SULLIVAN, J.E., “Further Investigations into the gramming Language Measurement”, Proc.FJCCAFIPS, Vol. Complexity of Software”, MITRE Technical Report 2874, 35, 1971. Vol II, 1974. STROUD, J.M., “The Fine Structure of Psychological Time”, Anals ELSHOFF, J.L., “An Analysis of some Commercial PL/1 Programs” of the New York Academy of Sciences, 1966, p.623. IEEE Trans, on Software Engineering, vol. SE-2, No. 2, June ZIPF, G.K., “Human Behaviour and the Principle of Least Effort”. 1976, pi 13. Reading, M.A., Addison-Wesley, 1949. ELSHOFF, J.L., “Measuring Commercial PL/1 Programs using Hal ZWEBEN, S.H., “A Study of the Physical Structure of Algorithms”, stead’s Criteria”, ACM SIGPLAN Notices, 11,5,May 1976, IEEE Trans, on Software Engineering, Vol. SE-3, No. 3, May p.38. 1977, p.250.
Book Review
J. Gruska, Mathematical Foundations of Computer Science 1977, delightful variety of fonts whose quality correlates very strongly (volume 53 of Lecture Notes in Computer Science), with the country of affiliation of the authors. Springer-Verlag, Berlin/Heidelberg/New York, 1977, xi + The papers are of two kinds. The first is the survey article, 595pp. $17.20. which summarizes a body of recent research work. Much of this work is not yet available in the accessible literature. The other kind This book constitutes the proceedings of the sixth symposium of paper presents new results, often referring the reader to technical in the series bearing the title “Mathematical Foundations of reports for more details. The quality of the papers in such a volume Computer Science”. The symposia in this series have been held can be expected to have a high variance, but the mean here seems to alternately in Poland and Czechoslovakia, the first being in 1974. be good. Since the papers address a large number of narrow topics, The proceedings of the third, fourth and fifth symposia have the overall effect is a sort of pointillist picture of the state of appeared as earlier volumes of the Springer Lecture Notes in research in the area in (eastern) Europe in 1977. Computer Science series. Thus the market for this book is essentially limited to libraries The latest proceedings deals with the symposium held in of institutions which do serious research in theoretical computer Czechoslovakia in September 1977, and contains 15 invited papers science. (Only monsters of omniscience and book reviewers are and 46 short communications. About 80% of the papers fall in the likely to want personal copies.) This book and, more generally, three broad areas of automata and formal languages, computational those of its type, are recommended for such places because they are complexity and theory of programming. Those remaining are made the principle means by which the Australian researcher, tyrannized up of several papers concerned with computability theory or by distance, can keep abreast of research developments. (highly) theoretical aspects of information storage and retrieval, and This point is well illustrated by the following example. a scattering of papers in other theoretical areas. Smyth’s important work on powerdomains was summarized in the Almost all the authors are from Europe, with a strong bias proceedings of the fifth symposium in this series, which appeared in towards eastern Europe. The invited lecturers are all respected 1976. It referred to a technical report also published in 1976. That researchers; their contributions average 14 pages. The short report appears in the February 1978 issue of the Journal of communications, averaging 8 pages, were not formally refereed, but Computer and System Sciences. were chosen by the program committee from 117 submitted papers. Paul Pritchard All papers are photo-reproduced. The resulting volume boasts a Australian National University
86 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Is Disciplined Programming Transferable, and is it Insightful?
By Charles Lakos and Arthur Sale
This paper examines the disciplined programming methodology of E.W. Dijkstra which advocates the development of correctness proofs simultaneously with writing a program, (if not before) in the context of two problems which faced the authors recently. The paper applies the thought processes advocated by Dijkstra to these problems and indicates the insights that the authors gained from this. In both cases algorithms new to the authors were derived, and the properties of these are also examined. The paper should be interesting to those concerned with increasing the effectiveness of programming, for it demonstrates that the techniques advocated by Dijkstra are indeed transferable to other programmers, and that this transfer yields better insight into the activity we call programming. KEYWORDS AND PHRASES: Disciplined programming, programming methodology, tree traversal, text searching, algorithm analysis, correctness proofs. CR CATEGORIES: 3.74, 4.0, 5.24.
1. INTRODUCTION Obviously readers who have carefully read this work will The purpose of this paper is simple: it is to benefit from our discussion, as perhaps will those who have demonstrate that the programming techniques advocated skimmed the ideas which are most apparent. However, so as by E.W. Dijkstra in ‘A Discipline of Programming’ are not to neglect the rest of the computing community, we (a) transferable to other programmers, feel we have to try to express some of what it is we are (b) useful and insightful, and promoting: (c) important. (a) the notion that developing a correctness proof Such a simple aim is however very difficult to achieve, since simultaneously along with the act of programming is we have to steer a narrow course between rigorous the best way to program; formality and loose reportage. The first will lose us readers (b) the promotion of clear thought in programming, we wish to interest in these ideas, while the second will including the expression of exactly what •conditions disgust computer scientists with a taste for formality. (post-conditions, pre-conditions, loop-invariants, etc) We have therefore chosen to describe attacks on two are supposed to hold at any particular execution quite distinct problems, illustrating how we came by them point of a program; and how we tackled them, at a level of description which is (c) the acquisition of some useful design rules which aid intermediate between the two extremes indicated above. the programmer in generalizing a given post-condition Our description of invariants and correctness proofs are (the statement of the problem) so as to develop a aimed to be understandable to ordinary programmers so as program that automatically particularizes the to make the paper generally useful, but leaving sufficient generalization; and hints and clues so that the formal gaps can be filled in (d) the removal of obsessions with control flow by the without difficulty by those with the necessary expertise. introduction of guarded commands which are The two problems we shall illustrate are quite executed only when the corresponding (boolean) common programming situations, and were not contrived guard conditions are true, and then sometimes for the purpose. In fact they arose independently in the without strict sequencing requirements. course of the work of each of the joint authors. We shudder at the simplication of the above, but Nevertheless they serve as admirable examples of the power hope that it will help. In most of what follows, the point of clear thought in programming and, we hope, illustrate of (d) is not relevant, and the major Dijkstra construct we the development of correctness proofs together with the act shall use (a simple do-od loop) can be given an exact of programming. The first example calls for traversing a tree equivalent in a conventional programming language, Table 1. data structure (commonly found in symbol tables, file The point behind the do-od loop in its full generalization hierarchies, search situations, databases, and many other and in these equivalents of a simple case lies in three simple places), while the second looks at the problem of searching facts: a piece of text for occurrences of a given word or phrase (a) there is some logical condition (a loop invariant) (increasingly important in information retrieval). which is true when the loop is entered, every time It is impossible to encapsulate all the ideas expressed around it, and when it is left; in ‘A Discipline of Programming’ in this introduction for (b) each time around the loop some finite progress is readers unfamiliar with Dijkstra’s work; indeed it would be made towards a definite goal (this ensures naive to think anything less than a book would do. termination); and (c) when the loop terminates we know the guard “Copyright © 1978, Australian Computer Society Irie. General permission to republish, but not for profit, all or part of condition (just b above) must be false. this material is granted, provided that ACJ’s copyright notice is We shall also have occasion to use Dijkstra’s if-fi construct. given and that reference is made to the publication, to its date of In this construct, the guards (boolean conditions) are issue, and to the fact that reprinting privileges were granted by evaluated and the statement corresponding to one of the permission of the Australian Computer Society.” * true guards is executed (an error occurring if there is no *Both with the Department of Information Science, University of Tasmania. Manuscript received 31st January 1978. Revised version received 10th May 1978. The Australian Computer Journal, Vol. 10, No. 3, August, 1978 87 Is Disciplined Programming Transferable
TABLE 1 2.1 A First Problem: Traversing a Tree Tree structures occur quite frequently in computing DO-OD LOOP problems, and the first program to which we wish to apply Dijkstra’s ideas arises from a need to traverse a tree (or in do b * other words, to apply some procedure to every node of the si; tree structure). Examples of practical situations where this s2; is needed often occur in system software: (a) if a compiler symbol table is stored as a tree od; structure, then printing its contents is a tree traversal problem; and PASCAL EQUIVALENT (b) if file names in an operating system are qualified by a hierarchy of directory qualifiers, then inspecting all while b do files in an automatic archiving process is also a tree begin traversal problem. si; Recursive algorithms to solve this traversal problem are s2; well-known, and easy to derive, since a tree structure is a recursively defined data structure. To make the problem end; more interesting, and the solution more useful, we shall look for non-recursive programs to solve this problem. This FORTRAN EQUIVALENT will make it usable in FORTRAN and assembly code environments. 1 IF (.NOT. b) GO TO 2 To make the succeeding development simpler, we si need to define some notation. Let us agree to describe our s2 programs in a PASCALTike notation, so that we can describe the procedure heading of the program we are GO TO 1 trying to write as: 2 procedure traverse (T:tree ; procedure P); and it is supposed to apply the procedure P to every node of the tree pointed at by T in turn. Since the representation true guard). Since all our programs use guards which are of the tree is of minor importance for the algorithm, we mutually exclusive, we can give another equivalence which shall simply use the following notation to access parts of will suffice for this paper (see table below). We should however add a warning that if we explain Dijkstra’s the tree T (derived from a notation of J.B. Hext, 1972). constructs this way, this does not mean that the programs should be implemented directly by our equivalences. The NOTATION MEANING notation is currently one for thinking in, not for coding. •«T the value of the root node of T ST the degree of the root node of T (i.e. TABLE 2 the number of subtrees) T[l] the first subtree of T IF-FI SELECTION T [2] the second subtree of T T[n] the n-th subtree of T if bl +sl; □b2 * s2; 2.2 Massaging a Recursive Algorithm □ ... To contrast approaches, we shall first employ a fi; classical approach. Since the problem is trivial if recursion is allowed, this immediately suggests starting with a recursive PASCAL EQUIVALENT program and manipulating (“massaging”) it into a non-recursive form. Accordingly, let us start with the if bl then si following recursive solution to the problem, which you else if b2 then s2 should understand before we go further:
else aborttheprogram; procedure traverse(T:tree; procedure P); {recursive version R1} FOR TRAN EQUIVALENT var i: integer; begin {process the root node} IF (.NOT. bl) GO TO 1 P(ocT); si {process the subtrees } GO TO 99 for i:=l to ST do 1 IF (.NOT. b2) GO TO 2 traverse (T [i], P); s2 end; [of procedure traverse} GO TO 99 This simple algorithm effects a traversal by subtrees. In n STOP 7777 other words, for every node in the tree, the first subtree of 99 that node is completely traversed before the second subtree and so on. Thus with the tree of Fig. 1 the order of
88 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Is Disciplined Programming Transferable
Thus, in eliminating the recursive procedure call, the call itself will be replaced by code to load the current values of T and i onto the stack, reset T (as the new “parameter”) and jump to the start of the procedure (the new “recursive call”). Then at “procedure exit”, values of T and i must be unloaded and the loop continued. However, since it is not normally possible to re-enter a loop construct once it has been exitted, the loop is rewritten using if and goto statements. In other words, the loop
for i := 1 to 6T do S;
is rewritten as i := l; loop: if i < 5T then begin S; i := i+1; goto loop; Figure 1 A tree example end; traversal of nodes is: A,B,E,F,C,D,G. In contrast, a traversal by levels would traverse all the nodes at level 0 before the nodes at level 1, etc. Then the These transformations result in our first non-recursive node order for the above example would be: solution (Nl). A,B,C,D,E,F,G. To produce this latter ordering is generally regarded as more involved since the processing cuts across the natural definition of a tree in terms of subtrees. One 01 procedure traverse (T:tree; procedure P); normally expects the tree to be differently represented if 02 {non-recursive version Nl} traversing by levels is to be an important operation (Hext, 03 label start, subtree, exit; 1972; Knuth, 1968). We shall not consider this point 04 var i: integer; further until we reach section 2.4. 05 S : stack; Returning to the recursive algorithm, if we are to 06 begin make it non-recursive then the normal approach (cf Bird, 07 clear(S); 1974) is to make explicit what has so far been implicit — 08 start: {process root and then initialize for subtrees) the stack which has held the activation records. To simplify 09 P(«T); the discussion we define the following stack primitive 10 i:=l; operations: 11 subtree: {try next subtree unless all have been processed} 12 if (i <5T) then 13 begin- NOTATION MEANING 14 {save current position and try next level} 15 load(S,T,i); clear(S); stack S is initialized to be 16 T:=T [i]; empty 17 goto start; 18 end; load(S,a1,a2,...) loads ,a2, etc. onto stack 19 {no more subtrees — go back a level } S in a left- to right order. 20 if empty(S) then goto exit; 21 unload(S,T,i); unload(S,a1,a2,...) unloads ai ,a2, etc. from stack 22 i:=i+l; S in a right-to-left order. 23 goto subtree; 24 exit: empty(S) a boolean function that returns 25 end; {of procedure traverse} true if stack S is empty, and false otherwise.
While this algorithm is certainly effective, it may offend The stack operations which have so far been implicit in the those of us with an aesthetic sense with its liberal recursion must now be made explicit. They consisted of sprinklings of goto statements. Can these be eliminated? If saving parameters and local variables on the stack prior to we look at the control flow of the program we have written the procedure call and restoring them at procedure exit. (Fig. 2), it breaks up into two overlapping loops. We can The tree parameter (T) and local variable (i) are the only achieve a tidier solution either by nesting loop2 within items which change with each procedure invocation and loopl, or vice versa. The results of these two approaches are therefore they are the only ones that need to be saved on given below; the latter solution requires the loading of a our stack. dummy value.
The Australian Computer Journal, Vol. 10, No. 3, August, 1978 89 Is Disciplined Programming Transferable procedure traverse(T:tree; procedure P); {non-recursive solution N2} label exit; var i : integer; S: stack; begin clear(S); while true do begin {process root and initialize for subtrees} P(*T); i:=l; 13- 18 {find next subtree to be processed} while (i > 5T) do begin if empty(S) then goto exit; 11-12 unload (S,T,i); i:=i+l; end; f save position and try deeper level} load(S,T,i); 21 - 23 T:=T [i]; end; exit: end; {of procedure traverse} 19-20 procedure traverse(T:tree; procedure P); {non-recursive solution N3} var i : integer; S : stack; begin exit {initialize stack and process the root} clear(S); load(S,nil,0); P(aT); Figure 2 Control flow of program Nl i:=l; {continue while subtrees remain} while not empty(S) do encountering a sentinel placed in the tree thus making begin redundant the test for an empty stack. (This is the sort‘of follow subtree approach taken by Wirth, 1976). while (i <5T) do Program N3 has its flaws too. For example it contains begin a dummy load onto the stack simply to satisfy the { save position and go a level deeper.} boundary conditions. load(S,T,i); So,' we have derived two non-recursive tree traversal T:=T[i]; algorithms by transforming a recursive solution. The P(«T); principal advantage of such an approach is the simplicity of i:=l; the original recursive solution, and our confidence in its end; correctness. If all the transformation steps can be proven to {no more subtrees — go back a level} be allowable, then the original together with the steps can unload(S,T,i); be considered to be a correctness proof for the i:=i+l; end-program. As such this is a respectable and very useful end; technique. Unfortunately, the transformation process can end; {of procedure traverse) be long and involved if an attractive end-product is desired. This massaging serves also to decrease our confidence in the correctness of the final solutions, for each manipulation As this now stands, N2 appears to be the less attractive must preserve the essential nature of the process and its solution: it contains an extra goto statement together with correctness. Can you be as confident that N2 and N3 are the unattractive construct “while true do ..(or forever correct as you can be about Rj ? do .. .). Yet if the tree traversal is to be a search for a This is a very serious objection to the transformation particular node (“nut” say) then the outer loop of N2 process, since it will manifest itself in a debugging problem becomes if we cannot be certain that our programs are indeed “while (aT A nut) do .. correct. This is exacerbated in the example by the This modified form of N2 is the one derived by J.B. modifications making the transformed algorithms look little Hext (1972). It is also the one which can be modified so like the original R.1; this introduces uncertainty as to the that the search can always be guaranteed to terminate by precise significance of each statement.
90 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Is Disciplined Programming Transferable
2.3 Starting from Scratch finite one, termination is guaranteed. Since we are then We therefore propose to attempt to derive a assured that the guard condition is false, it follows that the tree-traversal algorithm using Dijkstra’s notation and invariant taken together with: thought patterns (as far as we can reproduce them). After not empty(S) = false this has been done, we.can compare the results. Any readers i.e. empty(S) = true who are familiar enough with Dijkstra’s ideas are urged to implies the desired postcondition . It only remains to fill attempt their own solutions to the problem before reading in the details of ‘stack the subtrees’, and this is simply further since this is sure to increase awareness of the tasks done: involved. Following Dijkstra’s methodology, we should look at {Dijkstra style version D1} what is to be achieved, and formulate an appropriate {initialize, establish PI} post-condition which is capable of being generalized in clear(S); moving back further from the end-result. Suppose we take load(S,T); this simply as: do (not empty(S)) •> unload(S,T); P(*T); Rj = all the tree nodes have been processed i:=5T; {stack the subtrees} To achieve this post-condition, it is not difficult to deduce do (i 0) * that one or more loops are going to be required, but the load(S,T [i]); choice of loop invariants is not quite as obvious. From our i:=i-l; experience or intuition, let us suggest that a stack is going od; to play some part in this algorithm. (For consistency we od; shall retain our earlier programming style and stack primitive operations; for although it is trivial to turn these into Dijkstra’s vector operations, this will destroy some of Readers will have noted that the subtrees are stacked in the structure of what we are doing.) A stack is normally reverse order, so that they will be unloaded, and therefore used to record partially processed items, and so it appears processed by P, in left-to-right order. (In other words we natural to suggest that an appropriate invariant for an outer are preserving the behaviour of our earlier algorithms in loop of the program would be: that the first subtree is processed before the. second, etc.). You may be struck, as we were, by the simplicity of the solution. Furthermore, the derivation was supported by Pj = the stack holds the trees still to be processed theoretical considerations, and we are guaranteed of its (with the understanding that if a tree is correctness by our reasoning. Our level of confidence that recorded as unprocessed, all its subtrees are this solution is correct is much higher than with the version unprocessed too j N2 or N3. Having created a solution, we might still try to improve on it. We observe, for example, that we could Clearly then, the loop will continue while the stack is not improve the storage efficiency of the algorithm. Each time empty. Hence we arrive at the program fragment following, around the outer loop we save all the subtrees (as pointers which is written in a blend of Dijkstra’s notation and perhaps) on the stack. Instead we could record a pointer to PASCAL: the root node, and the number of the next subtree to be processed: this is similar to our approach in converting algorithm Rj to Nj. Then if we assume a pointer and an {put the tree on the stack - establishes PI) index take the same storage space, we shall use less stack clear(S); space if the average node branching ratio is less than two. load(S,T); (In fact, with a homogeneous tree of degree d and height h, do (not empty(S)) -> h-i . [remove an unprocessed tree } this approach uses (2xh) stack elements and 4 .2 d1+1 unload(S,T); {process the root node] stack accesses whereas the earlier solution used a maximum P(*T); of (dxh — h+1) stack elements and 2 ^ d‘ stack accesses.) {re-establish PI}'
The initial load directive establishes the invariant to begin with. Then, each time around the loop, the next subtree to P2 = the stack contains an indication of the subtrees be processed is removed from the stack, its root is to be processed, such that a pair, (T, ij on the processed, and its subtrees are stacked for later processing, stack implies that subtrees Tfi], Tfi+lJ, . .. thus re-establishing the invariant Pj. 7/577 are still to be processed. It is not difficult to see that the loop will terminate since the number of nodes to be processed decreases by one each time around the loop. Therefore provided the tree is a The results in the program:
The Australian Computer Journal, Vol. 10, No. 3, August, 1978 91 Is Disciplined Programming Transferable
{Dijkstra style version D2} even trees! Let us explore the possibility of replacing the {initialize - establish P2} stack in algorithm Dj by a queue. To do this we shall need clear(S); some new primitive queue operations: POT); {save indication of subtrees) if (6T = 0) skip; NOTATION MEANING 0 (ST > 0) load(S,T,l); open(Q) queue Q is initialized to be empty, fi; do (not empty(S)) •> jointQ.a!^,. • •) • add ai, a2, etc to queue Q in left- unload (S,T,i); to-right order. {save remaining subtrees, if any) leave(Q,aj,a2,.. .) remove at, a2, etc from queue Q in if (i = 5T) ^ skip; left-to-right order, D(i < ST) load(S,T,i+l); empty(Q) a boolean function that returns true fi; if queue Q is empty, and false {follow this subtree} otherwise. T:=T[i]; {process its root} We can now derive program version D4: POT); {Dijkstra style version D4,} {and save its subtrees} open(Q); if (ST = 0) •> skip; join(Q,T); • D(6T > 0) * load(S,T,l); {initialized, established PI} fi; do (not empty (Q)) •> od; leave(Q,T); P(*T); We make one final observation. The algorithm D2 is i:=0; formulated in terms of subtrees. Since the entire tree is not {enqueue the subtrees} itself a subtree, the root must be processed outside the do (iAST)* loop. To eliminate this the invariant must again be altered i:=i+l; giving P3 (below) with the resulting solution D3. join(Q,T [i]); od; P3 = the tree T (provided it is not nil) is still to be od; processed, so are the subtrees indicated on the stack, where (T,i) on the stack implies that To illustrate the conversion of this Dijkstra-like notation subtrees T[i+1], T[i+2], .. . T[8TJ are still to into a practical program, a PASCAL program equivalent to be processed. it is given in the Appendix. Astonishingly perhaps, this solution turns out to be a {Dijkstra style version D3} significant one — it results in the tree being traversed by clear(S); levels, instead of subtrees. The result is simple, beautiful, do (T =£ nil) * and apparently not widely known. We referred to traversal {process a node} by levels in section 2.1, and indicated that the common POT); view was that this required a special data-structuring, so {and its subtrees} that the structure should reflect the operations commonly load(S,T,0); required. Here however the transition has been achieved T:=nil; almost painlessly: apparently the only price to pay is the D (T=nil) and not empty (S) •> size of queue required whose maximum size is proportional {process a subtree} to the maximum width of the tree. unload (S,T,i); i:=i+l; 2.5 An Examination of this Problem if (i<5T)* So far we have been considering the production of a load(S,T,i); non-recursive algorithm for tree traversal. We found that if T:=T[i]; we modified a simple recursive solution, the indirect nature □ (i >5T) ■> of the approach meant that we did not have a very good {subtree completed} grasp of the end-product, and consequently our confidence T:=nil; level in our ability to avoid mistakes (in proof or in coding) fi; suffered. od; In contrast, the use of Dijkstra’s approach to programming, once we had mastered the change in 2.4 Using a Queue thought-pattern required, yielded better results — the When algorithm Dj was originally derived, the use of resulting programs were neater and the accompanying a stack seemed ‘natural’, preconditioned as we were by the development of a proof while we were programming meant existence of other known solutions. However, the form of that we could be very confident of the result. As an added derivation of this version highlighted an obscure possibility: bonus, we found that the same basic solution could yield what other structures could be used to hold subtree either a traversal by subtree, or a traversal by level, information as yet unprocessed? Clearly stacks, queues, and depending on whether a stack or a queue was used to store
92 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Is Disciplined Programming Transferable the unprocessed subtrees. The discovery of this new (to us This is a famous problem and many algorithms have been at least) solution is directly traceable to our better devised to tackle it. We can first exhibit the most obvious understanding of what we were doing, and of the decision solution, which is one which appears to be derived by most freedom we had at each point. beginning programmers faced with this problem. It is interesting to go back and ask ourselves where we went wrong in our traditional derivation of tree traversal algorithms, for the recursive algorithm Ri exhibits the same {simple-minded search: version SI} compelling elegance as the Dijkstra-style algorithm D,. for i:=l to (M-N+l) do Indeed, this is the clue, for the two algorithms are very begin similar and have the same invariant and proof structure. j:=0; The only essential differences are that Rx processes one while (j N) cand (text [i+j] = word[j+l]) do node and initiates the processing of the associated subtrees begin each recursive activation whereas Dx does this each time j:=j+l; round the outer loop. Other than that, they are identical. end; They both reflect the basic unit of the data structure, viz. a if (j = N) then P(i); node with a set of subtrees. The more we depart from this end; ideal and the more we become obsessed with control flow and the details of the algorithm, the messier our programs It should not need much explanation, except perhaps for become and the weaker is our grasp of what the algorithm the connective cand (conditional-and). This connective is was trying to do. We think that such insights must be similar to the familiar and for logical algebra, except that chalked up as a plus for the techniques we used because the the right term of a cand is evaluated only if the left term discipline of identifying and writing down the invariants proves to be true. Assuming that if-then-else is evaluated and post-conditions allowed us to keep the basic tree straightforwardly, the following equivalence holds: structure in mind during the whole process, and consequently the derived programs reflected the structure (b 1 cand b2) = (if b 1 then b2 else false) of the data. By contrast, though it is not impossible to go from program Rx to our Dx, it is very easy to be Program Sx is however a very poor algorithm. Its best side-tracked by some detail of the transformation. performance requires it to inspect (M-N+l) characters, while its worst performance requires the inspection of text: approximately (M x N) characters. We have given this algorithm for comparison purposes, and because most NEVERTHELESS, THE THEME OF THE BIG BAD WOLF RECURS IN THE FOLK people seem to think of it first. It is instructive for the reader to prove it correct, and to deduce what properties of
LITERATURE OF EASTERN EUROPE. text and word evoke the best- and worst-case performances. Dijkstra, too, has tackled this problem in ‘A word: Discipline of Programming’, and a short but very perceptive chapter (No 18) is devoted to it. The solution naturally
THE proceeds by specifying a post-condition Rx from the statement of the problem, intuiting that a loop is needed, and generalizing Rx to give Dijkstra’s outer invariant R2: Figure 3 Illustrating the text-search or pattern-match problem. Rj = all occurrences of word in text have been processed by P.
3.1 The Text-Searching Problem R2= all occurrences of word which have its first As a second example, we shall look at the problem of character in any of text positions 1 to i have searching some text for occurrences of a particular (smaller) been processed by P. piece of text. Suppose that we have two objects declared: It is interesting to note in passing that this is exactly var the same invariant needed to prove Sx correct! Thereafter, text : array [1..M] of char; however, the two solutions part company. The word : array [1..N] of char; simple-minded search simply advances i by one (cautiously) each iteration, and uses none of the information which may Fig. 3 illustrates one possible situation. To make the have been obtained from previous match attempts. problem formulation general and similar to the previous Dijkstra’s program is however based on advancing i by as far one, assume that we are asked to apply a procedure P to as is safe to go based on the available evidence, and using every occurrence of word in text. Thus if we want simply that evidence also to begin matching as far advanced as is to count the occurrences, or print them in context, or take warranted. Necessarily this involves pre-analysis of the word some other action, we can supply particular versions of P to set up a table of safe increments d (indexed by the last for our needs. Thus we can define a PASCAL-like depth of successful matching), and Dijkstra gives also an procedure heading for the program we are going to write: algorithm to create this table. Since Dijkstra’s treatment is already available, we exhibit the algorithm for searching procedure search (text,word : array of char; without comment, except to say that it inspects of the M,N : integer; order of M characters in all cases, and that we have slightly procedure P); modified the solution to accord with our conventions.
The Australian Computer Journal, Vol. 10, No. 3, August, 1978 93 Is Disciplined Programming Transferable recent issue of the Communications of the ACM, and had {Dijkstra-search : version S2j been in draft form since 1975. The two algorithms differ in •^initialize table d>; some details which affect the average and worst-case i,j := 1,0; performances. Our concern is with program design, not do (i < (M-N+l)) + primarily with particular forms of the algorithm, and do (j ¥= N) cand (text [i+j] = word [j+1]) * interested readers are referred to this article for a version j:=j+i; which has a worst-case performance which is of order (M + od; N) while preserving the low number of probes for typical, if 0 = N) ■> P(i); text searches. Our future discussion will refer to the basic i,j :=i+d[j],j-d[j]; approach as the ‘skip algorithm’ since many characters in □(0 94 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Is Disciplined Programming Transferable {skeleton of skip family of programs : S3} D ['11]=3 {establish R3 trivially} i:=N; do (i < M) ■> ch:=text[i]; I l1! 1 H \ if (ch = word [N]) •» 1 It will be noted that once having attempted to identify i:=0; possible matches based on the last character of the word at {R4 has been established trivially } text [i], this version simply bases its increase of i on the do (i < (M-N)) ■> same criterion as the alternative command; i is increased as i:=i+N; much as possible based simply on the character at text[i]. The Australian Computer Journal, Vol. 10, No. 3, August, 1978 95 Is Disciplined Programming Transferable To fill out the ‘process all occurrences that include text [i] ’ {new search program : version S4} part, we can again use the insights provided by Dromey’s initialize table Z>; algorithm by passing straight on if the character is not initialize table F>; represented in the word. If it does occur in the word, {remember F must now include the last char} however, we need to carry out searches to see if there are i:=0; any complete matches here that must be processed by P. do (i < (M-N)) * There are many ways of handling this, and the one we i:=i+N; choose to illustrate the algorithm is to create a table Z select(Z,text [i] ,Q); which for every possible character holds a queue of records do (not empty(Q)) * which detail the actual position indices of that character in leave(Q,j); the word. If the character does not occur in the word, the base,count:=(i-j),0; corresponding queue is empty. For notational convenience, do (count + N) cand ((base+N) < M) cand we shall also define the following basic operation on this (text [base+F [count+1 ] .index] table: = F [count+1] .c) ■> count :=count+l; NOTATION MEANING od; if (count = N) * P(i-j+l); select(Z,ch,Q) selects the queue for character ch in table □ (0 < count < N)skip; Z and makes a local copy in queue Q. fi; od; od; We again suspect that a loop will be useful in 3.4 Efficiency and Other Reflections processing the possible occurrences, and so we need to Clearly the new algorithm S4 we have derived is not a generalize our invariant still more, suggesting that it ought skip algorithm. It is easy to prove correct, but it is more to be: efficient? There is not room here to reproduce an analysis of either of the skip algorithms contained in the two previous papers, nor to analyse this new one, but it can be said that they all perform similarly. As N becomes very R5 = all occurrences of word which include the large, they all reach a situation where the average ‘stride’ characters at text positions N, 2xN, 3xN,.. . , i through the text (measured as M/(no of inspections)) tends have been processed except for those which to the same limit. This limit is determined by the character correspond to having the character text[i] in probability distributions in the two objects, which may not the word positions noted in the queue Q. be the same. We have not therefore been able to find a better algorithm, though we have found a different one. It is also interesting to note that the additional space This now allows us to write the following program fragment requirements of all algorithms grow proportionally to N; we to replace our outlined section: have omitted to discuss algorithms which have space requirements which grow faster or which require other expensive space requirements. Again, we reflect, the necessity of having to write (process all occurrences that include text[ij:} down and formalize our invariants has led to clarity of select(Z,text [i] ,Q); thought. While we were looking for algorithmic twists to {R5 is now established trivially} improve performance, the clarity with which we could view do (not empty(Q)) -* the choices provided us with a wide range of options. With leave(Q,j); the experience we gained, we found a clean and simple way 96 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Is Disciplined Programming Transferable That we produce algorithms which are novel to us is type not important; for all we know they are already buried treepointer = ♦ treenode; somewhere in the literature. What is important is that we treenode = record were led to discover them in natural ways, and that in each value : valuetype; . case we could express a high degree of confidence in the degree:integer; correctness of the resulting algorithm. Debugging programs subtree: array [1 .. degree] of treepointer is not an activity either of us pursues very often, and we end; perceive that we can reduce its frequency even further. We had, too, an ulterior motive. All too many procedure traverse(T: treepointer; procedure P); industry programmers are likely to be put off by the first {this is version D4 converted to a particular PASCAL purpose} few chapters of Dijkstra’s book. We hope that by var illustrating what can be done in a less formal way, some i : integer; programmers may be encouraged to probe deeper into what Q ; queue; we consider to be very important ideas. Though there begin remains much work to be done (when is there not?), we open(Q); think the orientation important enough that we are join(Q,T); teaching it as part of our undergraduate coursework. The while not empty (Q) do ideas will be in the marketplace quite soon .. . begin leave(Q,T); 5. REFERENCES P(T ♦ .value); BIRD, R.S. (1977): “Notes on Recursion Elimination”, CACM, Vol for i:=l to T t .degree do join(T,T♦ .subtree [i]); 20, No. 6 pp434-439. end; BOYER, R.S. and MOORE, J.S. (1977): “A Fast String Searching Algorithm”, CACM, Vol 20, No. 10 (October 1977), end; {ofprocedure traverse) pp762-772. DIJKSTRA, E.W. (1976): “A Discipline of Programming”, The second example is a procedure to implement a Printice-Hall. version of the skip search algorithm. It is written in a DIJKSTRA, E.W. (1976): “Formal Techniques and Sizeable Programs”, Lecture Notes in Computer Science. 44 EC1 slightly extended PASCAL to permit notational flexibility. Conference, 1976. DIJKSTRA, E.W. (1975): “Guarded Commands, Non-determinancy procedure search (text,word: array of char; and Formal Derivation of Programs”, CACM Vol 18, No. 8, M,N: integer; pp453-457. DROMEY, R.G. (1977): “Quicksearch - An algorithm for fast procedure P); keyword searching in text”, Paper submitted to CACM, obtainable from the author, University of Wollongong. label 1; GRIES, D. (1977): “An illustration of current ideas on the var Derivation of Correctness Proofs and Correct Programs.” IEEE, Trans. Soft Eng. SE2 4, 238-244, 1976 + correction in i,j : integer; p.262 May 1977. ch,lastch: char; HEXT, J.B. (1972): “Data Structures”, unpublished lecture notes D : array [char] of integer; circulated to students at the University of Sydney. begin KNUTH, D.E. (1968): “The Art of Computer Programming - Volume 1 - Fundamental Algorithms’, Addison-Wesley. {set up table D} WIRTH, N. (1976): “Algorithms + Data Structures = Programs”, for ch:=chr(0) to maxchar do D[ch] := N; Prentice-Hall. for i:=l to (N-l) do D[word[i] ] :=(N-i); { set up lastch for efficiency} 6. APPENDIX: PASCAL EQUIVALENTS OF lastch:=word[N]; FINAL SOLUTIONS {establish R3 trivially} In this appendix, we give equivalents of some of the i:=N; Dijkstra-style programs we derived in the body of this paper while (i < M) do for two pragmatic purposes: begin (1) to illustrate the process and make it apparent that ch:=text[i]; useful programs can really be produced this way, and if (ch = lastch) then (2) to make the algorithms and our arguments more begin {this is an occurrence of the last character} accessible to readers who may not be familiar with j:=(N-l); Dijkstra’s notation. while (j =£ 0) do The first example is an equivalent of the D4 version of tree begin traversal; it is presented as a procedure with some if (text [i-N+j] ¥= word [j]) then goto 1; surrounding type declarations in a slightly extended PASCAL to supply a context: end; P(i-N+1); 1: end; {advance i under invariance of R3}*- i:=i+D[ch]; end; {of while} end; {of procedure} The Australian Computer Journal, Vol. 10, No. 3, August, 1978 97 Port Management in the CYBER76-CSIRONET Interface * By B.J. Austin The paper describes the port management techniques which have been found necessary between CSIRONET and the CYBER76. Contention mechanisms exist between independent halves of CSIRONET, by way of separate PDP11 Host Interfaces. Central processes providing interactive or remote job entry service are provided with separate sets of ports, as are parallel versions under development. Error recovery procedures provide for failure of a central process or a PDP11 Host Interface. KEYWORDS: Computer networks, host interfaces. CR CATEGORIES: 4.3, 2.9 Introduction throughout the paper. The PPU is a 12-bit 4092-word The Division of Computing Research (DCR) has minicomputer. In the CYBER76 SCOPE environment, a interfaced the C.S.I.R.O. Network (CSIRONET - see PPU is assigned only one task, and the controlling code is Holden and Paine [1971] and Holden [1972] ) directly to loaded at system startup time and thereafter is normally a Control Data Corporation CYBER70 Model 76+ without continuously resident. In other CYBER series computers, any large scale frontend computer. the PPUs are operated as an assignable pool, in which any All other CYBER76 installations using the standard PPU can temporarily assume any required function. The CDC operating system (SCOPE) require a frontend CYBER76 PPU can most accurately be viewed as a driver computer, usually a CYBER70 or 170. The direct module, with a single dedicated function. connection between the CYBER76 and CSIRONET In order to avoid widespread changes to the SCOPE replaces the DCR-developed 3600 frontend (see Austin, system, access between a CPU program and the PPU is Ewens and Hudson [1976] ). made to appear like a magnetic tape and therefore uses the This paper describes a small facet of the total task of standard Tape Queue Manager (TQM). CYI is the central interfacing CSIRONET to the CYBER76, namely the process which manages interactive access while RIO harldles management of logical I/O “ports” between them. The all RJE peripherals. TEST CYI and TEST RIO are earliest implementation of remote terminals on the 3600 development versions running in parallel. Each of these (see Austin and Holden [1967] ) required a detailed processes is a job executing in central memory. They have knowledge of the network equipment configuration within been structured as user-level jobs, with additional priveleged the central computer. Since then the trend has been to primitives, including access to the path to CSIRONET. The move all such detailed knowledge into the network, and at path consists of two pseudo tapes — one for input and one the present time only a very general specification of the for output. Addressing of a particular port is achieved by a availability of remote batch devices exists in the central header byte within the data for output, and TQM has been computer. CSIRONET presents a number of “ports” to the modified to allow a port to be specified on a READ central computer, and manages the connection of these request. In both cases, data records are preceded by a ports to actual devices. The maximum number of ports 4-byte header giving port number and record length*. allowed is only a fraction of the total number of physical The PPU is controlled by code which interfaces to devices, and a port thus becomes an allocatable resource SCOPE (in central memory) as a standard SCOPE tape which requires management. The management process is driver, but the code is a completely new module intended designed to cater for two or more independent CSIRONET to interface to CSIRONET. CYI, RIO etc are permitted to interfaces, each of which may fail or be taken out of service output, in a single transmission, records for different ports, for maintenance. It also provides for parallel running of which may in fact be allocated to different PDP11 Host standard software and new versions under development by Interfaces. The PPU will separate these, and will output managing special “test” ports. each record as a single transmission. The PPU reformats the header information, but the data portion is passed through Overyew transparently. Figure 1 gives an overview of the interfacing setup. Port The PDP11 Host Interfaces are connected physically Management occurs in a CYBER76 Peripheral Processing to the PPU channel adaptor by hardware interfaces built by Unit (PPU), and the PDP11 computers connected'directly DCR. These interfaces allow a 12 bit code to be sent with a to it. These PDPll’s will be referred to as Host Interfaces “CONNECT” or “FUNCTION” command, and a 12 bit + The CDC CYBER70 Model 76 will be referred to as a CYBER76 “STATUS” response can be set by PDP11 software. The throughout the remainder of the paper. CONNECT code is used to address the required port, while FUNCTION and STATUS are used to acknowledge “Copyright © 1978, Australian Computer Society Inc. General permission to republish, but not for profit, all or part of successful/unsuccessful transmissions. The port number this material is granted, provided that ACJ’s copyright notice is used by a central process to address a given device is not the given and that reference is made to the publication, to its date of same as that used between the PPU and a PDP11, and a issue, and to the fact that reprinting privileges were granted by * All header and data formats are in multiples of 8 bit types. Coded permission of the Australian Computer Society.” data is always ASCII. *Division of Computing Research, Commonwealth Scientific and Industrial Research Organisation, Canberra, A.C. T. Manuscript received 30th March 1978. Revised manuscript received 7th June 1978. 98 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 . . . Port Management PDP 11/10 CHANNEL CSIRONET HOST INTERFACES ADAPTOR POP 11/10 TEST RIO 500 CONSOLES TEST CYI 180 RJE DEVICES Figure 1 Overview major part of the PPTTs task is to perform the translation. uniqueness is achieved by forming a CONNECT code from There are two reasons for this mapping, which may a port number (9 bits) and a PDP11 ordinal (3 bits). The seem redundant since the PDP11 Host Interfaces perform hardware interfaces are constructed so that they only an additional translation to actual device addresses. Firstly, respond to a CONNECT having with their identifying each central process is given a separate set of ports, ordinal. Each interface has the 3-bit identifying ordinal numbered from 0, so that test versions need not contain hardwired into it, and CONNECT signals not including this any special code to run in test mode. Secondly, and more ordinal are ignored. This is the standard approach adopted importantly, there must be a dynamic mapping function in CDC 3000-type equipments. within the PPU if all of the CSIRONET load is to pass An additional type of port has been established for through only one PDP11 Host Interface during periods of control purposes. Since all transmissions occur as a result of equipment outage or maintenance. a READ or WRITE command from a central process there In passing a record from a central process to a PDP11 is a lack of symmetry between the CYBER76 and or vice versa, the PPU must translate the port number CSIRONET sides of the interface. CSIRONET controls the within the header byte from one space to the other. The flow of data via a special “interrupt” port. This is given a length field (16 bits) is also reformatted to cater for the fixed CONNECT code and is read by the PPU wherever a reversed numbering of PDP11 bytes. hardware interrupt bit is set. Items read from the interrupt The PDP11 Host Interfaces each have 28K of port are not passed immediately to a central process, since memory, much of which is used for buffer space. They that requires a READ to be set up, but are stored within operate under the NODECODE system (see Holden and the PPU. Port O of each central process is used by that Paine (1971) and Holden (1972)), which uses a PDP11 process to read interrupt items directed to it. Each central macro language assembled on the CYBER76. process must poll regularly, since no provision exists in The Host Interfaces do not manage RJE devices SCOPE for sending an asynchronous signal to a running job individually, since this task is assigned to the “fanout” without locking out the I/O path to other jobs. machines (also with 28K of memory) at another level The PPU has storage only for one interrupt of each within CSIRONET. Connection between Host Interfaces type (Ready to Receive or Ready to Send) per port, with and fanout machines is made using wide bandwidth lines no queueing ability. The content of the tables associated usually TELECOM 48Kb/s group band circuits. For the with each port is given later (under Internal Tables). purposes of this paper an RJE device does not constitute a port, but in affect a “wide band line” multiplexing data for Interrupt Processing many RJE devices becomes one of the allocatable units. Interrupt items are 4 bytes long, and are very similar in format to the headers on data blocks. A port number in Types of Port the CSIRONET space is given and also a 16 bit length field. Ports allocated to CYI or TEST CYI are of type A control byte defines the type of item, of which there are “console” — i.e. devices used interactively. Ports allocated three at present. These are:— to RIO or TEST RIO are of type “wide band line” — i.e. a Ready to receive “length” bytes. logical circuit which corresponds to all or part of a Ready to send “length” bytes. TELECOM group band circuit. Wide band line Log off. transmissions contain an internal block structure which The first two will eventually cause a WRITE or READ from addresses RJE devices, but the PPU is not cognisant of this the CYBER76, and are only of concern to this paper in that structure. For the purpose of this paper, console ports or they can imply port allocation (or reject if no port is wide band line ports are treated equally, although available). The PPU determines the type of port by finding differences in block size and other matters of usage exist. the range of port numbers in which it falls, and searches the In the CSIRONET port numbering space fixed ranges allocation table of the appropriate central process to find it have been defined for ports which may be allocated to CYI, if already known. If not, a spare entry is allocated, and its RIO, TEST CYI or TEST RIO. These would be regarded as ordinal within the array becomes the port number to the having types “console”, “wide band line”, “test console” central process. The length and direction information is and “test wide band line” respectively. Each PDP11 Host stored and will be cleared when the central process polls its Interface uses the same ranges of ports, and within the PPU interrupt port. The Australian Computer Journal, Vol. 10, No. 3, August, 1978 99 • • • Port Management Log off searches for and clears an entry with the occur during scheduled maintenance periods. Apparent given CSIRONET port number. This breaks the mapping failure is detected by lack of response from the hardware between the CYBER76 and CSIRONET ports. Note that interface or failure to commence data transmission. log off is initiated by a PDP11 Host Interface, and is Consecutive occurrences of these symptoms are counted, intended to be accompanied by clearing of CSIRONET and PDP11 failure is presumed after a count of 63. The tables linking the port to a physical device. count is on a port-by-port basis, and each port exceeding In all cases, the search for a given port number may the limit is cleared to the log off state. In this state, READ fail, implying that a free port must first be allocated. If no or WRITE commands are accepted by the PPU without any free ports exist, a reject signal is sent to the PDP11 and error response, but no data transfer with CSIRONET processing of any further interrupt items is abandoned. This occurs. This mechanism was provided within the PPU, but crude reject mechanism was necessary because of the could have been partly achieved by error retry procedures limited memory of the PPU. It is the only contention within the central processes. However, CYI blocks records mechanism between the independent PDP11 Host for many ports into a single transmission, and undoing this Interfaces. Within these PDPll’s, partially processed blocking in error cases would have proved difficult. Also, a interrupt records must be retransmitted, and overheads are central process has no way of deallocating a port without reduced by limiting the number of new port allocations to CSIRONET cooperation. The detection of PDP11 problems one per second. can fail if the abovementioned specific symptoms do not occur. In this case it is possible for a PDP11 Host Interface Internal Tables to be allocated all or most of the ports, with no good Every port has five 12 bit table words associated with recovery mechanism. At the moment, no PPU initialisation it in the PPU memory. The tables are ordered by CYBER76 procedure is invoked by a reload of a PDP11 Host port number, and there are, in effect, separate tables for Interface, but it is proposed to send a log off signal on each each central process. port to the PPU. This would make PDP11 reload Information held is:— symmetrical in treatment to a CYI/RIO restart. Equivalent CSIRONET port number No complete mechanism has been provided so far for Ready to receive length PPU restarts. These are very infrequent, but can be initiated Ready to send length by SCOPE after PPU memory parity error or other failure. Error countdown The PPU is reloaded with all its tables cleared, and a restart Miscellaneous bits (particularly indicating presence of signal is sent to the PDP11 Host Interfaces. The net result is interrupts) as catastrophic as a full CYBER76 restart, since the Last operation trace (for debugging). connection between a console or wide band line and the Currently, a total of 192 ports are allowed for. This controlling central process is broken. An interactive user number could be increased by about 200 in the memory would feel much as if the SCOPE system had been available. restarted. The effort required to preserve the port Management in failure situations allocation tables is considerable and has not been deemed Ports, particularly those associated with interactive worthwhile. Since the code has been debugged, it has been devices, are in a very dynamic state, as users log on or log necessary to restart the PPU approximately once every 3-6 off. Any mechanism which causes ports to remain months, and usually it has been done in conjunction with erroneously allocated very rapidly leads to a state in which other failures, such as in PDP11 Host Interfaces. new log ins are prevented. Failure situations such as a restart of a central process (which leaves the PPU tables Conclusions untouched) will give rise to “No port available”, and Mechanisms have been developed to manage a limited mechanisms have been developed to cater for each case. number of ports between the CYBER76 and CSIRONET. Timeout of idle ports has proved a very powerful tool. These mechanisms handle contention and failure situations Timeout is used to log off an idle interactive (CYI) satisfactorily. The techniques used, especially timeouts, port after 10 minutes of inactivity. The log off is initiated seem ad hoc and it may be that a more general solution by CYI, and follows the same series of steps as a normal could be found. Nevertheless, removal of detailed user-requested log off, viz:— CYI sends a log off signal to knowledge of network configuration from a central CSIRONET, CSIRONET clears the physical connection and computer and the possibility of connecting further sends a log off command to the PPU. If the user inactivity computing or other facilities to a single network makes port is in fact due to a break in the communication path at the management a very real issue. The development of the PPU PDP11 Host Interface, a further mechanism described code has been assisted by the CYBER76 architecture and below is needed since CYI will be unable to send a log off the debugging facilities provided for such work. It is signal to CSIRONET. RIO also uses timeout on idle wide normally possible to checkout PPU code quite safely with band lines. This always indicates communication or the production system running, and this technique was used equipment failure since blocks are sent continually even if extensively in the initial stages. Now that CYI and RIO no actual RJE load exists. constitute production systems, short periods of dedicated Restart of CYI is signalled by an attempted log off on checkout time are required if a new version of the PPU all ports. Ports which are not, in fact, allocated within the code is being installed. The original implementation was PPU tables give an error reject to CYI, and no log off signal written as a program disjoint from SCOPE, but is now fully is sent to CSIRONET. RIO restarts cause the RJE traffic on integrated into the operating system source code. each active wide band line to be recommenced. An error handling mechanism within the PPU has Acknowledgements been provided for the case of apparent failure of one of the The development of the CYBER76 - CSIRONET FDP11 Host Interfaces. These apparent failures can also interface has involved many people within DCR but three 100 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 . . . Port Management deserve special mention for their involvement at the level the DAD System”, Australian Computer Journal, Vol. 1, described by this paper. John Paine was responsible for the P201. AUSTIN, B.J., EWENS, P.M. and HUDSON, R.H. (1976): “Linking PDP11 side of the interface while Henry Hudson and Peter a CYBER76 to a 3600”, Software - Practice and Experience, Ewens developed the central process interfaces (CYI and Vol. 6, P541. RIO respectively). HOLDEN, T.S. and PAINE, J.E. (1971): “The CSIRO Computing Network” Proc. DECUS Australia Symposium, PI 19. HOLDEN, T.S. (1972): “A communications network for scientific References computing”, Proc. Fifth Australian Computer Conference, AUSTIN, B.J. and HOLDEN, T.S. (1967) “Recent Developments of P112. An Overview of Programming Practices By J. M. Yohe The following was,an omission from the .above paper that appeared in the May 1978 issue of The Australian Computer Journal. APPENDIX A: A PROGRAMMER’S CHECKLIST □ d. Recheck of code □ e. Check of keypunching or other transcription Program □ f. Desk check of program Programmer □ g. Compilation/assembly/loading (diagnostic) Date Started Date Completed □ h. Test data prepared □ 1. Problem specifications prepared and checked with □ i. Debugging originator □ j. Program verification □ a. Statement of problem □ 7. Revision of algorithms, flowcharts, code, etc. □ b. Input/output specifications □ 8. Documentation □ c. Restrictions and constraints □ a. Problem statement □ 2. Algorithms and data structures selected and checked □ b. Algorithm and data structure descriptions □ a. Search for existing algorithms — check of □ c. Program logic and structure description suitability □ d. Program listing (commented and sequenced) □ b. Search for existing programs □ e. Testing procedure write-up (including test data □ c. Development of specialized algorithms listing) □ d. Verification and error analysis of algorithms □ f. Operating instructions □ e. Selection of data structures □ f. Consultation □ 3. Selection of language(s) APPENDIX B: PROGRAM MAINTENANCE □ 4. Program logic and structure CHECKLIST □ a. Modularization □ b. Flowcharts — organization Program □ c. Flowcharts — neatness and readability Programmer □ d. Module structure Date Started Date Completed □ e. Debugging design □ 1. Documentation of error □ 5. Coding □ a. Symptoms □ a. Module labeling □ b. Conditions under which it occurs □ b. Statement labeling □ 2. Determination of necessary corrections □ c. Variable names □ a. Check that proposed repair will work □ d. Source code formatting □ b. Check effect of proposed repair on rest of □ e. Organization of control and informational program statements □ 3. Checkout of correction □ f. Comments and visual impact □ a. Desk check □ g. Flexibility □ b. Compilation/assembly/loading (diagnostic) □ h. Code written legibly, confusing characters □ c. Test data prepared distinguished □ d. Debugging □ i. Use of standard language; nonstandard □ 4. Documentation statements isolated □ a. Errata to problem specifications □ j. Input and output data formats □ b. Errata to algorithm descriptions □ k. Code checked □ c. Errata to program logic and structure □ 6. Checkout descriptions □ a. Review of problem statement □ d. Errata to program □ b. Review of algorithms/data structures □ e. Errata to operating instructions (if any) □ c. Review of program logic and structure □ 5. Distribution of correction The Australian Computer Journal, Vol. 10, No. 3, August, 1978 101 A SNOBOL4 Program to Clean up FORTRAN Source By John D. Blackburn* A computer program written in SNOBOL4 is presented which sequentially renumbers a FORTRAN source program, and improves its legibility. KEYWORDS: SNOBOL4, pattern matching. CR CATEGORIES: 4.22, 4.41 INTRODUCTION compilers now accept an extended FORTRAN. The Several programs to renumber sequentially a standard program has run successfully on the UNIVAC 1106, PDP FORTRAN program, and to generally improve the 10 and the ICL 1906A, the latter with SPITBOL, the legibility, exist, and this program makes no claim to SNOBOL4 compiler. originality. TIDY and POLISH from the University of SNOBOL4 is essentially a language oriented towards Colorado are two of the best known. However, many of searching for patterns of any complexity. A FORTRAN these programs do not guarantee that all the statements will cleansing program is itself basically a pattern searching and be renumbered correctly, or that some will not be ignored. replacement program. Diagram 1 depicts the flow of the This program does make such a claim. program, and this flow-chart is largely self-explanatory. The renumbering program written in SNOBOL4 is Pattern matching is made considerably easier if all* shown in Fig 1, and sample input and output are shown in blanks are deleted in the input line. In FORTRAN, blanks Figs 2 and 3 respectively. The program was developed on are ignored entirely except in Hollerith strings. In order to the UNIVAC 1106 under the EXEC 8 operating system at prevent significant blanks in Hollerith strings from being the Wirtschafts- und Sozialwissenschaftliches TABLE 1. Unique Characters to Determine Type Rechenzentrum Wien (Austria), although the program of FORTRAN Statement shown here was run on a DEC System 10 at the University of Essex (England). No. of Characters Type of Statement 5 SKIP FILE SKIP RECORD The Program 4 COMMON In addition to the statemen number in columns 1 COMPLEX through 5, the following statements are renumbered: READ REAL DO loop 3 ENCODE ASSIGN statement END unconditional GOTO ENTRY computed GOTO REREAD REWIND assigned GOTO 2 ACCEPT logical IF ASSIGN arithmetic IF BACKSPACE ENCODE and DECODE BLOCKDATA CALL input and output DATA The FORTRAN source is via the card reader, and the DECODE reformatted FORTRAN is sent to the card punch. DIMENSION DOUBLE PRECISION Classification of FORTRAN Statements EQUIVALENCE EXTERNAL Sale (1971) in a succinct article on the classification FIND of FORTRAN statements presents an algorithm for ANSI FORMAT FORTRAN, and his algorithm is fully implemented in the FUNCTION IF SNOBOL4 program. In addition to the statements IMPLICIT identified by Sale, most non-ANSI FORTRAN statements INTEGER are included in the program, since it has been ten years PAUSE since ANSI recommended a standard FORTRAN, and most PRINT PUNCH STOP “Copyright © 1978, Australian Computer Society inc. SUBROUTINE General permission to republish, but not for profit, all or part of 1 GOTO this material is granted; provided that ACJ’s copyright notice is LOGICAL given and that reference is made to the publication, to its date of NAMELIST issue, and to the fact that reprinting privileges were granted by TYPE permission of the Australian Computer Society.” WRITE *lnstitut fur Hohere Studien und Wissenschaftliche Forschung Vienna, Austria. Manuscript received 18th January, 1977. Revised version received 10th May, 1978. 102 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Snobol4 Program to Clean Up Fortran Source START READ CARD STOP CARD:= NEXT LASTCARD OUTPUT COMMENT CONCATENATE READ NEXT TO CARD NEXT LASTCARD:= XES COMMENT REMOVE COLS CONTINUATIOl 1-6 OF NEXT REMOVE HOLLERITH FROM CARD Diagram 1. Flowchart of the Program (continued next page) The Australian Computer Journal, Vol. 10, No. 3, August, 1978 103 Snobol4 Program to Clean Up Fortran Source DELETE BLANKS RENUMBER COLS 1-5 IFPART:= NULL OUTPUT FIRST ^ REPLACE LETTER IMPLIES HOLLERITH ■—AS SIGNMENT,— DO LOOP CLEAN UP .SSIGNMENT ACCESS UNIQUE LETTERS IFPART LOGICAL CARD:= REST JUMP Diagram 1. Flowchart of the Program 104 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Snobol4 Program to Clean Up Fortran Source removed, all strings in the source FORTRAN statements are DO integer variable = both , removed, stored and replaced by %n% where n is the nth which succeeds only at the comma. string encountered. Thirdly, assignments are searched for with the pattern A first prime signals a possible prime enclosed string. variable = For a Hollerith string, the pattern and = I . I / I * I , I (integer H variable ( anything ) = would locate both from the beginning of the source statement, which X=2H- would locate TEST=X.NE. 1H+ DO 101= 10.0 F0RMAT(1H ,5HTITLE) and and READ(5,10)=.TRUE. DATA/VALUE/1 HI/NEXT/4* 1H-/ . respectively. The string presents a problem in the case of the At this point, the source statement must be a embedded string, viz: FORTRAN command. The type of FORTRAN statement X=5H‘ YES’ can be uniquely determined by, at most, the first five and characters, as shown in Table 1. A jump can now be made Y- 3HYES’ to the correct “clean up” pattern. It would be superfluous To avoid accessing the wrong string, a scan is made to present in detail the way in which each FORTRAN for both possibilities where the position of H and the first statement is reformatted. Essentially, blanks are inserted prime is sufficient to determine the correct type of string. where their absence would obscure intellegibility. Before the edited source statement is output the removed References strings are replaced. AMERICAN NATIONAL STANDARDS INSTITUTE (1966) ANSI Through the &ANCHOR = 1 instruction, patterns are FORTRAN, (X3.9-1966). forced to match from the first character of the source DORRENBACHER J. (1974). “POLISH A Fortran Program to Edit Fortran Programs”, Technical Report CU-CS-050. University statement, and thus matching in the centre of the statement of Colorado. is avoided. GRISWOLD, R.E. et al (1971), The SNOBOL4 Programming At first, the first letter is tested against Language, Prentice Hall. MURPHY, H.M. (1966), “TIDY Program”, University of Colorado H,J,K,M,0,Q,U,V,X,Y and Z since these letters can only Program. refer to assignments. SALE, A.H.J. (1971), “The Classification of FORTRAN Secondly the DO loop is tested with the pattern Statements”, Computer J., vol 14, pp 10-12. SNOBOL4 (VERSION 3.4.3. JAN. 16, 1971) DIGITAL EQUIPMENT CORP., PDP-10 * * A SNOBOL4 PROGRAM TO CLEAN UP FORTRAN SOURCE * 1 DEFINE ('SN(OLDNUMBER)') STORAGE SPACE FOR 1000 DIFFERENT STATEMENT NUMBERS AND 200 DIFFERENT STRINGS PER SOURCE STATEMENT OLD = ARRAY (10#) STORE = ARRAY (2#) DEFINITION OF INTEGER, VARIABLE AND BOTH 4 NUMERIC = '1234567890' 5 ALPHA = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' 6 ALPHANUMERIC = ALPHA NUMERIC 7 INT = SPAN(NUMERIC) 8 VAR = ANY(ALPHA) SPAN(ALPHANUMERIC) I ANY(ALPHA) 9 BOTH = SPAN (ALPHANUMERIC) 1 11 TYPE = 'INTEGER' I 'REAL' I 'LOGICAL' I 'COMPLEX' 12 EXT = '*2' I '*4' I '*8' I '*16' 13 IO = READ' I 'WRITE' I 'PRINT' I 'PUNCH' I 'ACCEPT' I 13 'TYPE' I 'READ' I 'FIND' 14 DECLARE = 'FORMAT' I 'DIMENSION' I 'COMMON' I 'EXTERNAL' I 14 'DATA' I 'EQUIVALENCE' I 'NAMELIST' 15 TERM = 'ENDFILE' I 'REWIND' I 'BACKSPACE' I 'STOP' I 'PAUSE' Figure 1. The Program (continued next page) The Australian Computer Journal, Vol. 10, No. 3, August, 1978 105 Snobol4 Program to Cl ean Up Fortran Source 16 SUB = 'SUBROUTINE' I 'FUNCTION' I 'ENTRY' 17 OTHER = 'G' I 'AS' I 'IF' I 'CA' I 'BL' I 'DO' I 'IM' I * 17 'SKIPF' I 'SKIPR' * * CONSTANTS * 18 SPECIAL = ANY('=.,/*(') 19 QUOTE = " "' K = ',' 20 * * INITIAL STATEMENT NUMBER AND INCREMENT * 21 INITIAL = 10 22 INDEX = 5 23 TOTAL = 0 * * BUILD PATTERNS FOR FORTRAN STATEMENTS # 1 : DO LOOP * 2 : COMPUTED & UNCONDITIONAL GOTO * 3 : LOGICAL & ARITHMETIC IF * 4 : ASSIGN 24 DO = 'DO' INT. NUM (VAR '=' BOTH K) . REST 25 CGOTO = 'GOTO' BAL . EXP 26 GOTO = 'GOTO' INT . NUM 27 IF = 'IF' BAL . EXP 28 IFGOTO = 'GOTO' INT . NUM RPOS(o) 29 IF3 = INT . N1 K INT . N2 K INT . N3 30 ASSIGN = 'ASSIGN' INT . NUM 'TO' VAR . V * * READ SOURCE STATEMENT * IF COMMENT, OUTPUT AND READ NEXT STATEMENT * IF CONTINUATION, CONCATENATE TO PREVIOUS STATEMENT * NEW STATEMENT SHOWN BY BLANK OR ZERO IN COLUMN 6 * * N IS NTH HOLLERITH STRING * 31 START N = 0 32 CARD = INPUT : F( END) 33 AGAIN CARD LEN(1) . COMMENT 34 PUNCH = 1 DENT(COMMENT,'C') CARD : S(START) 35 NEXT NEXT = INPUT : F(LAST) 36 NEXT LEN(1) . COMMENT 37 IDENT(COMMENT,'C') : S(STRING) 38 NEXT LEN(5) LEN(1) . CONT REM . REST 39 CONT ' ' I '0' : S(STRING) 40 CARD = CARD REST : (NEXT) 41 LAST LASTCARD = 'YES' * # TEST FOR HOLLERITH STRING (NH AND ' ') * 42 STRING &ANCHOR =0 43 PRIME = 2000 44 HOLL = 2000 45 CARD (QUOTE @PRIME BREAK (QUOTE) QUOTE) . LITERAL 46 CARD SPECIAL . A INT1 . B'H'@HOLL 47 SKIP = HOLL - 1 48 EQ(PRIME,HOLL) : S(FIVE) * * REPLACE HOLLERITH STRING BY %N% WHERE N, AN INTEGER, * IS THE NTH STRING ENCOUNTERED, PLACE IN STORE Figure 1. The Program (continued next page) 106 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Snobol4 Program to Clean Up Fortran Source 50 SKIP = LT(PRIME,HOLL) PRIME - 1 : S(QUOTE) 51 D = B 52 BLANK D ' '=' ' : S(BLANK) 53 CARD A B ('H' LEN(D)) . LITERAL 54 QUOTE STORE * REMOVE ALL BLANKS & SET 'IFPART' TO NULL * 60 REMOVE CARD' '=' : S(REMOVE) 61 IFPART = '' TEST DO LOOP AND ASSIGNMENT 62 REST &ANCHOR = 1 63 CARD ANY('HJKMOQUVXYZ') S(OUT) 64 CARD DO ='DO'SN(NUM) ' 'REST S(OUT) 65 CARD VAR '=' S(OUT) 66 CARD VAR '(' BREAK(')') ')=' S(OUT) * IF 'END' RESET INITIAL VALUE OF STATEMENT NUMBER * 67 IDENT(CARD,'END') : F(SIGNIF) 68 TOTAL = 0 69 OUTPUT = '...... ' : (OUT) JUMP TO SIGNIFICANT CHARACTERS 70 SIGNIF &ANCHOR = 1 71 CARD LEN(5) . SIG 72 SIG 'ENC' I 'DE' S(TRANS) 73 SIG 'IN' I 'L' I 'COMP' I 'REAL' S(TYPE) 74 SIG 'FO' I 'Dl' I 'EX' I 'DA' I 'COMM' I 'N' S(DECLARE) 75 SIG 'EQ' S(DECLARE) 76 SIG 'PR' I 'PU' I 'W' I 'READ' I 'T' I 'AC' S(IO) 77 SIG 'PER' I 'FI' S(IO) 78 SIG 'ST' I 'BA' I 'PA' I 'END' I 'REW' S(TERM) 79 SIG 'SU' I 'FU' I 'ENT' S(SUB) 80 SIG OTHER .JUMP S(£JUMP)F(OUT) ******************************************************************** * MAIN SEGMENT TO CLEAN UP FORTRAN STATEMENTS * ******************************************************************* **** UNCONDITIONAL GOTO * 81 G CARD GOTO ='GOTO'SN(NUM) : S(OUT) 82 CARD 'GOTO(' : F(ASSGOTO) * **** COMPUTED GOTO * 83 CARD CGOTO = ' ' 84 CARD K = ' ' 85 &ANCHOR =0 86 NEWEXP = ' ' Figure 1. The Program (continued next page) The Australian Computer Journal, Vol. 10, No. 3, August, 1978 107 Snobol4 Program to Clean Up Fortran Source 87 CG0T01 EXP INT . NUM = ' ' : F(CG0T02) 88 NEWEXP = NEWEXP SN(NUM) K : (CG0T01) 89 CG0T02 NEWEXP = '(' NEWEXP ')' 90 NEWEXP = ')' 91 CARD = 'GOTO ' NEWEXP ' CARD : (OUT) * ***** ASSIGNED GOTO * 92 ASSGOTO CARD 'GOTO' = ' ' 93 CARD BREAK(K) . LABEL K = ' ' 94 &ANCHOR =0 95 NEWEXP='' 96 ASSG0T01 CARD INT.NUM = ' ' : F(ASSG0T02) 97 NEWEXP = NEWEXP SN(NUM) K : (ASSGOT01) 98 ASSG0T02 NEWEXP = '(' NEWEXP')' 99 NEWEXP ',)' = ')' 100 CARD = 'GOTO ' LABEL K ' ' NEWEXP : (OUT) * ***** IF ***** FOR LOGICAL IF, TEST SECOND PART * 101 IF CARD IF = ' ' : F(OUT) 102 IFPART = 'IF ' EXP ' ' 103 CARD IFGOTO = 'GOTO ' SN(NUM) : S(OUT) 104 CARD IF3 = SN(N1) K SN(N2) K SN(N3) : S(OUT)F(TEST) * ***** ASSIGN * 105 AS CARD ASSIGN = 'ASSIGN ' SN(NUM) ' TO ' V : (OUT) * ***** CALL * 106 CA CARD 'CALL' BREAM'D . V = 'CALL ' V ' ' : S(OUT) 107 CARD 'CALL' = 'CALL ' : (OUT) * * * * * ENCODE & DECODE * 108 TRANS &ANCHOR =0 109 CARD BREAM'D • T (BREAK(K) K) . NC INT . NUM = ' ' 110 CARD (K BREAM')') ')') ■ V = ' ' 111 CARD = T " NC SN(NUM) V ' ' CARD : (OUT) * ***** IMPLICIT * 112 IM CARD 'IMPLICIT' (BREAM'D ■ T) = ' ' 113 CARD = 'IMPLICIT ' T " CARD : S(OUT) * **** INTEGER. REAL. LOGICAL & COMPLEX * 114 TYPE CARD TYPE . T 'FUNCTION' BREAM'(') • NAME = 114 * T' FUNCTION ' NAME ' ' : S(OUT) 115 CARD TYPE . T EXT. F = T E ' ' : S(OUT) 116 CARD TYPE. T = T' ' : (OUT) * ***** ENDFILE, REWIND, BACKSPACE, STOP & PAUSE * 117 TERI CARD TERM . T INT . NUM = T ' ' NUM : S(OUT) 118 CARD TERM.T = T ' ' : (OUT) * **** FORMAT, DIMENSION, COMMON, EXTERNAL, DATA, ***** EQUIVALENCE & NAMELIST * 119 DECLARE CARD DECLARE . D = D ' ' : (OUT) * Figure 1. The Program (continued next page) 108 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Snobol4 Program to Clean Up Fortran Source ***** BLOCK DATA, DOUBLE PRECISION, SKIP FILE & SKIP RECORD * 120 BL CARD 'BLOCKDATA' = 'BLOCK DATA' : (OUT) 121 BU CARD 'DOUBLEPRECISION' = 'DOUBLE PRECISION ' : (OUT) 122 SKIPF CARD 'SKIPFILE' = 'SKIP FILE ' : (OUT) 123 SKIPR CARD 'SKIPRECORD' = 'SKIP RECORD ' : (OUT) * ***** FORTRAN IV INPUT & OUTPUT * 124 IO CARD IO . A (')' BREAK(T) ')') . B = ' ' : -FOOD 125 &ANCHOR =0 126 B K INT. NUM = KSN(NUM) 127 B 'ERR=' INT . NUM = 'ERR=' SN(NUM) 128 B 'END=' INT . NUM - 'END=' SN(NUM) 129 CARD = A' 'B' 'CARD : (OUT) * **** FORTRAN II INPUT & OUTPUT * 130 101 &ANCHOR =0 131 CARD IO . A INT . NUM K = A ' ' SN(NUM)' ' : S(OUT) 132 CARD IO . A INT . NUM = A ' ' SN(NUM) ' ' : (OUT) * ***** SUBROUTINE, FUNCTION & EXTERNAL * 133 SUB CARD SUB.S = ' ' 134 CARD BREAK ('('). T = ' ' 135 CARD = S ' 'T' 'CARD : (OUT) * *************************************************************** * * REPLACE ALL HOLLERITH STRINGS * 136 OUT &ANCHOR =0 137 CARD = IFPART CARD 138 REPLACE EQ(N) : S(FIN) 139 CARD '%' N '%' = STORE * * IF STATEMENT LENGTH > 66 BREAK INTO SEVERAL * CARDS WITH + IN COL 6 FOR CONTINUATION * 141 FIN IDENT(CARD) : S(EOF) 142 PUNCH = LE(SIZE(CARD),66) STATE CARD : S(EOF) 143 REST CARD LEN(66) . PART REM . CARD : F(FIN) 144 PUNCH = STATE PART 145 STATE = ' +' : (REST) 146 EOF CARD = DIFFER (LASTCARD,'YES') NEXT : S(AGAIN)F(END) * ****************************************************************** * * SUB-PROGRAM TO RENUMBER STATEMENT NUMBERS * PRINT NEW AND OLD STATEMENT NUMBERS * WARNING PRINTED IF NO OF STATEMENTS EXCEED 1000 * 147 SN OLDNUMBER ' '= ' ' : S(SN) 148 I =0 149 CONVERT(OLDNUMBER, 'INTEGER') 150 EQ(TOTAL) : S(SN2) 151 SN1 I = LT(I,TOTAL) I + 1 : F(SN2) 152 IDENT(OLD Figure 1. The Program (continued next page) The Australian Computer Journal, Vol. 10, No. 3, August, 1978 109 Snobol4 Program to Clean Up Fortran Source 154 OLD NO ERRORS DETECTED IN SOURCE PROGRAM Figure 1. The Program C C FORTRAN PROGRAM THAT CONTAINS MOST NON-ANSI STATEMENTS C FUNCTIONJOIN(IA,IB) IF (I ABS( I A- IB). LT. 5) GOTO 25 JOIN=IA+IB 25 IF (SQRT(FLOAT(IA—IB))+FLOAT(IB)) 32,56,71 56 JOIN=1 RETURN 71 JOIN=2 RETURN 32 JOIN=3 RETURN END INTEGERFUNCTIONNUMBERf LIMIT) C INEFFICIENT ROUTINE TO SUM SERIES NUMBER =0 DO 56 l=3,LIMIT 56 NUMBER= NUMBER*! RETURN END C SUBROUTINEX(INPUT,FIELD,NUMBER,POS) COMMON START LOGICAL INPUT ,FIELD,START IF (INPUT) GOTO 678 IF (FIELD) 56,24,78 24 NUMBER=1 56 POS=10.0 ENTRY XMIN (INPUT) 78 IF (.NOT.(INPUT)) START= .FALSE. 678 RETURN END C C MAIN PROGRAM C IMPLICIT INTEGER (U-Z) INTEGER BINARY,IF(10) REAL* 8 RESULT,SETUP DIMENSION A{10) LOGICAL GOTO (20,20) INTEGER*2CASE1, C ASE2 EQUIVALENCE (ALPHA,BETA,GAMMA), 2 (X,Y,Z) COMMONA1,A2,A3 COMMON/GROUP1/DELTA,EPSI LN,SMALL NAMELIST/INPUT/P,Q,R EXTERNAL SIN C C VARIOUS INPUT AND OUTPUT Figure 2. Sample Input (continued next page) 110 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Snobol4 Program to Clean Up Fortran Source ENCODE(5,400,VAR) (A(l),l=1,5) WRITE(BINARY) A,B,C SKIP RECORD 10 READ(5 #1,149) A,B,C 149 FORMAT (3F1 0.0) READ(5,INPUT) REREAD 127, A,B,C WRITE (6,161) 161 FORMAT(1 H1, THIS PROGRAM WAS DEVELOPED AT THE', 1 ' WIRTSCHAFTS UND WISSENSCHAFTLICHFS RECHENZENTRUN IN', 2 'VIENNA, AUSTRIA'/'ON THE UNIVAC 1106 UNDER EXEC8') WRITE (KOUT,HK) Z,Y READ127,A,B,C READ (LDN,*)A,B,C FIND(LDN#I) WRITE (LDN,4,5,6) 456 FORMAT (1H,' DO 10 1=1,100 ') 127 FORMAT (3F10.0) DECODE (2,300 , VAR) ALPHA,BETA 400 FORMAT (80A1) 300 FORMAT (10F5.2) C I =4 IF(ITRUE) = 1 DO 181=1, 20 DO20I = 50. 0 18 CONTINUE 1 QUOTE= "" 19 4 TEST= 5HESSAI PROBLM=’FIG 8.5B' 119 TITLE = 15H'** ERROR ***' GOTO 17 15 GOTO 10=15.0 GOTO (10, 20) = X.NE. 1H+ GOTO (10,20,20) ,JUMP 10 IF (X.NE.95.) GOTO 14 G0T015 20 TYPE 105 105 FORMAT (1 HI,'SOLUTION') 115 CONTINUE 14 GOTO (11,25,25,11,11,25,25,11,25) NOKOMA 11 WRITE (KOUT,117) (A(l),l=1 , N) 117 FORMAT (1H , 10F4.1 ) READ (IN,117, END= 194, ERR= 15) B,C,D GOTO 119 25 ACCEPT 114,DUMMY 114 FORMAT (F10.0) C VARIOUS TYPES OF'IF'STATEMENTS IF (BOOLEX) WRITE(6,117)VALUE IF (Y.NE.Z) A(1)=10.0 IF (WORD .NE .6HVIENNA.OR.WORD.NE. 'PIPAIX')GOTO 18 IF (X.LE.5.) 1,10,15 IF (A(5) .LT.A(7)) CALLCHANGE (A(1 ),A(2)) IF (A(1 ).GE.A(2)) STOP2 IF (BOOLEX) GOTO (20,18,25, 24), JUMP IF (BOOLEX) ASSIGN115 TOLABEL IF (Y.GE.X**2) GOTO LABEL,(25,18,194,119 ) C 17 ASSIGN 119 TOLABEL Figure 2. Sample Input (continued next page) The Australian Computer Journal, Vol. 10, No. 3, August, 1978 111 112 Figure c c c c C C U r> C c Figure o o o o o o O o o o o 24 3a. 2. Sample Sample 25 20 10 15 25 20 10 15 10 REWIND CALL Input Output CONTINUE GOTO CALLTEXT STOP END SUB (continued LABEL, ITAPE WRITE SKIP VARIOUS READ ENCODE COMMON NAMELIST/INPUT/P,Q,R COMMON EXTERNAL EQUIVALENCE REAL*8 INTEGER IMPLICIT SUBROUTINE INTEGER*2 DIMENSION MAIN END POS=1 NUMBER=1 LOGICAL RETURN ENTRY COMMON IF IF JOIN=3 JOIN=2 JOIN=1 JOINHA+IB IF DO NUMBER=NUMBER*I LOGICAL END NUMBER=0 RETURN INEFFICIENT INTEGER END 1 RETURN RETURN FORTRAN RETURN IF IF FUNCTION (A,B,4HCITY,SIN) (.NOT.(INPUT)) (FIELD) (INPUT) (SQRT(FLOAT(IA (IABS(IA=IB).LT.5) 10 RECORD (18,25,119,115) next PROGRAM 0.0 (5#l,1 l=3,LIMIT (BINARY) XMIN RESULT,SETUP (5,10, page) A1,A2,A3 INTEGER /GROUP1/DELTA,EPSILN,SMALL GOTO(20,20) BINARY,IF(10) START INPUT INPUT,FIELD,START FUNCTION GOTO 15,20,25 PROGRAM JOIN SIN 5) CASE1,CASE2 A(10) (INPUT) X ROUTINE 10 VAR) A,B,C Snobol (ALPHA,BETA,GAMMA), (INPUT,FIELD,NUMBER,POS) AND (IA,IB) A,B,C 10 START=.FALSE. (U-Z) — (A(l),l=1,5) 4 NUMBER IB))+FLOAT(IB)) GOTO OUTPUT THAT Program TO SUM 10 CONTAINS to (LIMIT) Clean SERIES up The 15,2025 Fortran MOST (X,Y,Z) Australian Source NON-ANSI Computer STATEMENTS Journal, Vol. 10, No. 3, August, 1978 Figure p The U c C C o o o C Australian 3a. 60 115 110 100 105 Sample 95 90 80 85 65 45 40 35 75 70 20 30 55 50 25 # 15 Computer Output Journal, STOP WRITE ACCEPT TYPE TITLE=15H'** GOTO ASSIGN GOTO VARIOUS GOTO GOTO TEST=5HESSAI + CONTINUE CALL CALL CONTINUE GOTO GOTO(10,20)=X.NE.1H+ GOTO QUOTE="" + WRITE IF GOTO10=1 IF IF FORMAT READ FORMAT FORMAT CONTINUE DO END REWIND IF IF IF IF IF IF PROBLEM='FIG DO20I=50.0 IF(ITRUE)=1 FORMAT FORMAT FORMAT FORMAT I DECODE FORMAT IF REREAD READ FORMAT =4 WRITE WRITE WISSFI READ I READ FIND VAC (V.NE.Z) (BOOLEX) (Y.GE.X**2) (BOOLEX) (BOOLEX) (A(1 (A(5).LT.A(7)) (X.LE.5.) (WORD.NE.6HVIENNA.OR.WORD.NE/PIPAIX') (X.NE.95.) Vol. 40 85 TEXT SUB1 65 55 60 (IN, (95,100,1 (70,75,75), LABEL, 1=1,20 (5,INPUT) 10, ).GE.A(2)) (KOUT,105) (6,25) (LDN 1106 55 20, (LDN,*) 110, ITAPE (LDN, (KOUT,K) SCHAFTLICHES (2,35, 20, (F10.0) (1H No. (1 (10F5.2) (80A1 (3F10.0) (1H,' (1H1, (3F10.0) TYPES 5.0 105,END=50,ERR=65) TO A( H1,'SOLUTION') 45,70,65 A,B,C (A,B,4HCITY,SIN) UNDER A,B,C 3, WRITE DUMMY GOTO ASSIGN GOTO Nl) Snobol 1 , (40,1 ERROR VAR) LABEL 30) 1 August, )=1 #,95,95, GOTO ) THIS 0F4. 8.5B' DO A,B,C CALL STOP OF JUMP 0.0 #,55,90) Z,Y (A(I),I=1,N) 80 10 4 (75,40,1#,1 1) ALPHA,BETA 'IF'STATEMENTS (6,105) EXEC8') PROGRAM Program 90 1978 LABEL, 1=1,1# *** 2 CHANGE 1#,1 TO RECHENZENTRUN ’ VALUE LABEL to #95,1#), (1#,40,50,55) Clean ') 15), B,C,D WAS (A(1),A(2)) up Fortran JUMP DEVELOPED NOKOMA Source IN GOTO VIENNA, AT THE',' 40 AUSTRIA'/'ON WlRTSCHAFTS THE UND UN 113 Snobol 4 Program to Clean up Fortran Source 10 25 80 14 15 32 85 105 20 56 90 115 25 71 95 11 100 25 10 56 105 117 110 114 10 678 115 24 15 56 20 24 25 78 10 400 15 149 20 127 25 161 30 456 35 300 40 18 45 1 50 194 55 119 60 17 65 15 70 10 75 20 Figure 3b. Old and new statement numbers Book Reviews Meidman, M.J., McLeod, D.J., Pellicore, R.J. and Squire, M. RISS: algorithmic form. The chapters dealing with specifically computer A Relational Data Base Management System for orientated techniques such as sorting and random number Minicomputers, Van Nostrand Reinhold Australia, 1978, generation are good, but the remainder of the book does not cover 113pp. $18.50. anything like a representative range of O.R. techniques in sufficient detail. It is disappointing to find only the old standards like The book describes a DBMS named RISS implemented in the Mathematical Programming and Simulation (surely every O.R. Basic Plus language on a PDP 11/40 under RSTS/E. student and practitioner has access to computer codes for these) Chapters discuss the General Structure of RISS, the RISS rather than techniques that have been less well or often Naive-Level Interface, RISS Applications-Level Interface with two computerised. chapters giving the full implementation code. Each chapter has a good bibliography (again they all seem to The book will be of prime interest to those with PDP ll’s reference theoretical work) but the treatment of problem who feel the need for a Data Base Management System with fairly formulation and technique illustration is a fairly standard one and rudimentary facilities. There is a useful bibliography. thus rather disappointing. A.Y. Montgomery The book is fairly readable with occasional unnecessary Monash University recourse to jargon, cliches and new word invention. In summary, the book falls rather between two stools in that it probably does not satisfy the newcomer to the techniques nor the Arne Theseij, Computer Methods in Operations Research published novice O.R. programmer. Furthermore, the title suggests a book by Academic Press in 1978. pp. 268. A$20. that may provide the reader with some methods of applying O.R. techniques in a practical (computer) environment. This is not the The book has 11 chapters. The aim of the text is to “fill the case. However, from a theoretical viewpoint the text is apparently growing gap between computational requirements emerging in quite sound and has obviously been well researched. The potential modern industrial engineering and operations research (IE/OR) purchaser should thus look closely at the details of each chapter to applications and the algorithmic and computational methods ensure he is not misled. commonly available to the IE/OR student and practitioner”. The book is essentially a mainly theoretical treatment R.J. Willis, of a few operations research techniques that are then either Monash University embodied in the appropriate Fortran computer code or described in Dept, of Econometrics 114 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 A Criterion for Determining the Number of Groups in a Classification % X By D. A. Ratkowsky and G.N. Lance' A simple criterion is described herein for determining the number of groups in a numerical classification employing the three most commonly used attribute types, viz. qualitatives, multistates and numericals. Calculation of the criterion is presently available on the CSIRO Computing Network as an adjunct to RF.MUL, a divisive program with terminal reallocation, but the criterion is not specific to that program and can be calculated from the groups obtained from any classificatory algorithm operating on one or more of the above attribute types. KEY WORDS: Numberical classification, attributes, groups, mixed data. CR CATEGORIES: 5.4. INTRODUCTION THE PROPOSED CRITERION In an earlier communication (Lance and Williams To determine the “best” or “optimum” number of 1977), it was shown how the relative importance of the groups n into which the individuals should be classified, we attributes in the definition of inter-group structure could be propose the following simple quantity: assessed for mixtures, in any proportion, of nominal (including both “exclusive disordered multistate” and C/nI/2 “binary” or “qualitative”) and numeric (“continuous”) where C is the average value obtained by applying equation attribute-types. The conjecture rests upon a demonstration (1) to each nominal attribute, and its equivalent (B/T),/2 to of the compatibility between the definition of a degree of each numeric attribute. All attributes used for the purpose association for nominal attributes proposed by Cramer £f classification at the n-group level are averaged to obtain (1946, p.443) and a corresponding one for numeric C. The optimum number of groups is that value of n for attributes suggested by the analysis of variance. The Cramer which the measure C/n1/2 has its maximum value. The measure, applied to the number of individuals in each of reasoning which led to the development of this criterion is the states of the nominal attribute after a total of N given in Appendix 1. In the next section, we present six sets individuals have been classified into n groups, is as follows: of data which have served as examples on which the X2/N proposed criterion has been tested. C = min(s-l,n-l)_ (1) EXAMPLES OF USE OF CRITERION where x2 is the conventional chi-square measure of Example 1: Celmisia gracilenta complex (data association in a contingency table and min(s-l,n-l) signifies courtesy Dr D.R. Given). Measurements were obtained on the smaller of the two quantities s-1 and n-1. For numeric 275 specimens of plants for 11 numeric attributes and 6 attributes, a corresponding measure is (B/T)1/2, where B is binary attributes. Application of the program REMUL the between-group sum of squares and T the total sum of (Lance and Williams 1975) to classify the specimens, squares. Both measures are constrained to lie between 0 and followed by evaluation of C or its equivalent for each of the 1 and it was shown (Lance and Williams 1977) that they 17 attributes and the calculation of the mean value C of the give the same result for a binary attribute if on the one 17 values, gave the following results: hand the attribute is considered to be a categorisation and on the other hand it is considered to be a numeric attribute which can take only the values zero and unity. Since C is n C C/n1/2 applicable to multistate nominal as well as to binary 2 0.279 0.197 nominal, those authors argued that the procedure was fully 3 0.442 0.255 compatible for all the attribute types they considered. The 4 0.506 0.253 utility of the measure, which is bounded by zero and unity, 5 0.533 0.238 is that it can be employed to rank the attributes in the 6 0.581 0.237 relative order of their importance to the classification. Thus, three or four groups are indicated. These numbers of groups conform to what was independently suggested by “Copyright © 1978, Australian Computer Society Inc. considering field observations together with cytological and General permission to republish, but not for profit, all or part of ecological data (D.R. Given, pers.comm.). this material is granted, provided that ACJ’s copyright notice is given and that reference is made to the publication, to its date of Example 2: Parasuicide study (Henderson et al. issue, and to the fact that reprinting privileges were granted by 1977). Data on 350 parasuicide patients, 200 from Hobart permission of the Australian Computer Society.” * and 150 from Canberra, were obtained from answers given *CSIRO, Division of Mathematics & Statistics, Hobart; f CSIRO, Division of Land Use Research, Canberra. Manuscript received 13th April, 1978. The Australian Computer Journal, Vol. 10, No. 3, August, 1978 115 Criterion for Determining Number of Groups in a Classification by the patients to a schedule of questions put to them Number of Number of during treatment. From the original total of 15 binary, 134 groups groups multistate and 35 numeric attributes, a sub-total of 44, requested produced mostly numeric, attributes were used in the REMUL analysis. The following results were obtained: g n C C/n1/2 2,3 2 0.868 0.614 n C C/n‘/j 4,5 3 0.903 0.521 2 0.193 0.137 3 0.264 0.153 Thus, the 2-group result is clearly indicated, in agreement 4 0.287 0.144 with the earlier published findings. 6 0.318 0.130 Example 5: Lake Superior floristic survey (data 8 0.361 0.128 courtesy Dr D.R. Given). Data were collected at 47 sites, 10 0.391 0.124 which were to be classified on the basis of 50 binary attributes representing the presence or absence of the 50 Thus, three groups are indicated, conforming to what was most widespread species of plants. Results obtained using independently suggested using other cluster analysis REMUL are as follows: programs and techniques (Henderson et al. 1977). Two of these groups were clinically interpretable by the Number of Number of psychiatrists in the research team, whereas the motivation groups groups of the members of the third group could not be clearly requested produced interpreted. Example 3: Heavy metals in Tasmanian oysters g n C C/n1/j (Ratkowsky et al 1974). Data were obtained on 2 2 0.228 0.161 commercial and native oysters growing in 49 locations in 3 3 0.322 0.186 Tasmania, the attributes being 5 numeric variates 4,5,6 4 0.379 0.190 representing the mean zinc, cadmium and copper concentrations in, and the mean wet and dry weights of, The indicated number of groups is three or four. The best the oysters sampled at each location. In the earlier agreement with other classification procedures was published paper (Ratkowsky et al. 1974), an agglomerative obtained at the 3-group level. At this level, both REMUL hierarchical classification was carried out. The results of and ‘maximal predictive classification’ (Gower, 1974) this, together with a principal co-ordinate analysis, clearly produced a group of 27 stands relatively poor in species showed three groups, and these data thereby provide a numbers but these procedures differed somewhat in the critical test for the criterion proposed herein. The REMUL subdivision of the remaining 20 relatively species-rich algorithm sometimes produces less groups than the user stands. requests, i.e. one or more of the requested groups may be Example 6: Southwest Tasmania floristic survey (data empty. Empty groups occurred in each of the last four courtesy Drs R.K. Crowden and S.J. Jarman). 138 sites near examples, and necessitate adding an extra column to the the Gordon River in southwest Tasmania were classified on table of results, as below: the basis of 87 binary attributes representing the presence or absence of 87 species of vascular plants. Results obtained Number of Number of using REMUL are as follows: groups groups requested produced Number of Number of groups groups g n C C/n'4 requested produced 2 2 0.532 0.376 3 3 0.770 0.444 g n C C/n1/2 4,5,6 4 0.773 0.386 2 2 0.255 0.180 3,4 3 0.397 0.229 Thus, the criterion C/n1/2 unambiguously indicates the 5 4 0.445 0.222 3-group solution to be the optimum. 6 5 0.459 0.205 Example 4: European wasps Rhyssa persuasoria The indicated number of groups is three or four. The best (Spradbery and Ratkowsky 1974). Data were obtained on agreement with other classification procedures was 24 populations of wasps from Europe and North Africa, obtained at the 3-group level. At this level, both REMUL and the populations were classified on the basis of 3 and MULTBET (Lance and Williams 1967) produced a numeric attributes derived from the original measurements. small group of river-bank communities, an The study concluded that there were two major intermediate-sized group of predominantly button-grass geographical groupings; all classificatory programs that were communities, and a large group of rain forest and rain employed unanimously identified a group of four forest scrub communities. populations in southwest Europe and Morocco. Some geographical differences existed within the remaining 20 DISCUSSION populations but all had links with one or more adjacent The first two of the six examples given above populations. The results obtained, after use of REMUL, are contained a mixture of nominal and numeric attributes, the as follows: 116 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Criterion for Determining Number of Groups in a Classification next two involved only numeric attributes, and the last two sum of squares explained by the regression, but because it only binary attributes. The proposed criterion is thus increases the regression degrees of freedom at the same applicable to attributes of a single type, or to mixtures of time, the explained variance may actually decrease. An these attributes in any proportion. Although the criterion optimum number of terms could be defined as that number was evaluated in the present study in conjunction with which maximizes the ratio of the between to the total REMUL, it has no specific association with that program variance, i.e. and may be employed with any classification program that uses nominal and/or numeric attributes. REMUL was used B/(n-l) here to illustrate how one calculates the criterion because it T/(N-1) is the only program currently available on the CSIRO Computing Network which calculates the contributions of where N is the total number of cases, n is the number of each attribute to a_classification, the average of all such terms (synonymous with the number of groups in a cluster contributions being C and which is needed to calculate the analysis), and B and T are the between and total sum of proposed criterion. However, the program GROUPER squares, respectively. (Lance et al. 1968) has now been altered so that the C In the context of cluster analysis, the number of values, C and the proposed criterion can be calculated by individuals being clustered is constant for any given set of allowing the user to specify the membership of each of the groups obtained from other classification procedures. data, so the term N-l can be discarded. Further, as the square-root transformation is monotonic, one can maximize Furthermore GROUPER lists the attributes in rank order of the C values. [B/(n-l)T]1/2 instead. Since (B/T)1/2 is the In each of the examples presented here, the number continuous-attribute equivalent to the Cramer measure C, one obtains C/(n-l)‘/2. This applies to a single attribute of groups suggested by the proposed criterion appears to be only, and the most simple way of extending the formula to reasonable in that this number is either supported by other the full set of attributes^ used in the classification is to information or by other classification procedures. When various other clustering algorithms were employed on the replace C by its average C over all attributes. (We also tried averaging C2 rather than C, but this worked less well for the data in these examples, they tended broadly to group the examples described herein). As n was found to work better individuals in a similar fashion to_REMUL for the value of n than n-l in the examples studied, the final formula is C/n1/2. for which the proposed measure C/n1/2 was a maximum. For It should be clear that there is no underlying inferential values of n larger than this, group membership tended to basis for assessing this criterion in terms of a formal diverge widely. The proposed criterion can therefore be statistical test. Its value can only be determined by viewed as indicating the maximum number of groups for empirical application of the criterion to a variety of real which different classificatory algorithms are capable of data sets, as was done herein. agreeing broadly. For a larger number of groups, the widely different classifications obtained are a reflection of the REFERENCES well-established fact that numerical classifications are CRAMER, H. (1946). "Mathematical Methods of Statistics”, strongly dependent upon the algorithm that generates Princeton University Press: Princeton. them. EVERITT, B. (1974). "Cluster Analysis”, Heinemann: London. GOWER, J.C. (1974). “Maximal Predictive Classification”. APPENDIX 1 Biometrics 30, 643-654. HENDERSON, A.S., HARTIGAN, J., DAVIDSON, J., LANCE, Some Considerations Leading to the Proposed Criterion G.N., DUNCAN-JONES, P., KOLLER, K.M., RITCHIE, K., McAULEY, K., WILLIAMS, C.L. and SLAGHUIS, W. (1977). Several procedures for determining the “optimum” “A Typology of Parasuicide”. Brit. J. Psychiat. 131, 631-641. number of groups in a classification have hitherto been LANCE, G.N., MILNE, P.W. and WILLIAMS, W.T. (1968). “Mixed Data Classificatory Programs. III. Diagnostic Systems”. Aust. proposed (cf. Everitt 1974, pp.59-61, for a discussion of Comput. J. 1, 178-181. some of these), but all of these depend, for their successful LANCE, G.N. and WILLIAMS, W.T. (1967). “Mixed-data operation, upon certain restrictions either about the nature Classificatory Programs. I. Agglomerative Systems”. Aust. of the attributes (e.g. that they be continuous and normally Comput. J. 1, 15-20. LANCE, G.N. and WILLIAMS, W.T. (1975). “REMUL; A New distributed within clusters) or about the shape of the Divisive Polythetic Classificatory Program”. Aust. Comput. J. resulting clusters (e.g. that they be approximately 7, 109-112. spherical). More recently, Mojena (1977) proposed and LANCE, G.N. and WILLIAMS, W.T. (1977). “Attribute evaluated two stopping rules in association with the seven Contributions to a Classification”. Aust. Comput. J. 9, 128-129. most widely used hierarchical clustering strategies. MOJENA, R. (1977). “Hierarchical Grouping Methods and Stopping In the present work, attention is directed towards the Rules: An Evaluation”. Comput. J. 20, 359-363. development of a criterion that may be used with mixed RATKOWSKY, D.A., THROWER, S.J., EUSTACE, I.J. and data types and with non-hierarchical clustering procedures. OLLEY, J. (1974). “A Numerical Study of the Concentration of Some Heavy Metals in Tasmanian Oysters”. J. Fish. Res. Bd The Cramer measure enables one to treat continuous and Can. 31, 1165-1171. nominal attribute-types in a unified manner. We consider an SPRADBERY, J.P. and RATKOWSKY, D.A. (1974). “An Analysis analogy with multiple regression analysis, where the user of Geographical Variation in the Parasitoid Rhyssa persuasoria has to decide whether the inclusion of an additional variate (L.) (Hymenoptera, Ichneumonidae)”. Bull. ent. Res. 64, is justified. Adding an extra term will generally increase the 653-668. The Australian Computer Journal, Vol. 10, No. 3, August, 1978 117 Letters to the Editor OPEN LETTER TO AUTHOR course. The transaction cards are read directly onto a tape file which is sorted to enable the validation to take place in Mrs C.M. Prime, one pass of the master files. MLC Limited, A transaction for change of key (mentioned in 12 and PO Box 200, 3) is transformed into two transactions (as mentioned in 3) NORTH SYDNEY, 2060 before the initial sort above. After this initial sort, one of these two will then be in the correct position for the old Dear Mrs Prime, key and one in the correct position for the new key. In the Reference your ACJ, Vol. 9, No. 4 Paper validation run the former of these is used to check the validity of the old key and extract all other information ‘‘An Integrated System for the Administration of from the existing record. The latter is used to check that Managed Funds ” the new key is not the same as an existing record. There are a couple of things about your Integrated The information extracted from the existing record is System which mystify me:— transformed into transaction form, with the new key, in the 1. {Refer paragraph 2.1) — Do you manually sort the validation run. A further sort at the end of the validation Transaction Cards into Member Name Sequence within run places these manufactured transactions in the new key Policy Number (i.e. Member Master File Sequence) or if not position. The transaction file is then in its final form ready how do you achieve your validation with only a single pass for “file maintenance”. At that time, as far as the “change of the Fund Master and Member Master Files? (Surely if the of key” procedure is concerned, the transaction file will Transaction Cards are in random sequence on average about contain one transaction in the old key position for deletion half the tape will need to be read for each transaction. So of the incorrect record, and another (actually several other) your statement of only requiring a single pass of the Master in the new key position for setting up the correct record Files at Validation Time would not be true). Also how do with all the information previously in the incorrect record. you recombine the transactions on your Transaction Yours faithfully, Holding File if the Transaction Cards are not as I have C.M. Prime suggested? 2. {Refer Section 1.2 and Section 3, Paragraph 9) — The Editor, The problem of change of key value as for example when a Australian Computer Journal person’s birth date is changed. How does your system check at Validation Time that the new Key Value is not already on file (an unlikely situation but still possible) and if it Dear Sir, cannot check this how would an insertion for an existing My attention has been drawn to a statement Master record key be dealt with at File Maintenance Time? concerning the Australian Research Grants Committee in If you feel inclined you might care to write a letter to the editorial of the May 1978 issue of the Journal. It is the Editor of the ACJ to resolve these matters. there recorded that the Australian Computer Science Yours sincerely, Conference was told that the assessors whom the ARGC A. Y. Montgomery, invites to appraise grant proposals ‘discount completely Deputy Chairman, papers published in Australian journals and this includes the Dept, of Computer Science Australian Computer Journal. They are only willing to accept publications in overseas journals as evidence of AUTHOR’S REPLY prestigious research output’. This statement is simply not true. Naturally, there is a The Editor, hierarcy of esteem among publication outlets. Some Australian Computer Journal Australian journals stand well up in that hierarchy and many overseas journals do not. The ARGC’s ‘advice to Dear Sir, applicants’ offers the following observation, inter multa I refer to my description of “An Integrated System alia: ‘Assessors, especially those from overseas, sometimes for the Administration of Managed Funds” in the comment that they have not been able to consult the November 1977 issue of the Australian Computer Journal applicants’ publications because they have appeared in little and will now attempt to clarify a few queries which have known, poorly distributed journals or other publication been raised. media. Assessors also at times judge an investigator they do Perhaps I should mention that the whole description not know by the quality of the journals in which he of the system, including the flow-chart, is considerably publishes’. The italics are mine. simplified in order to highlight those aspects of the design Conceivably, this comment, born of experience, which, at the time, were innovative and which therefore might have given rise to the opinions quoted, but it is may present solutions to similar problems experienced by clearly not directed specifically against Australian other commercial systems designers. publications and still less is it particularized towards the In particular, the transaction cards are shown in the Australian Computer Journal. It just points out a fact of flow-chart as being fed directly into the validation run. life, and indeed the ‘advice’ goes on to say that ‘this is a Actually there are several intermediate steps omitted here, part of the whole of grantsmanship, and those who wish to which it was assumed would be more or less a matter of play the game should do their best to enter with as many 118 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 Letters to the Editor high cards as they can get their hands on’. 200-SELECT-PROCESS SECTION Incidentally, the ‘advice’ referred to is revised each 200. year, but the actual sentences quoted come from the pen of MOVE 1 TO SELECTION. the original author, Professor O’Neil of Sydney, who is a IF condition-1 psychologist. ADD 4 TO SELECTION. I hope your readers will be reassured that IF condition-2 publications in the ACJ will be viewed on their merits, ADD 2 TO SELECTION. moderated properly by the ACJ’s own standing. As a IF condition-3 chemist, I am happy to testify that publications in the ADD 1 TO SELECTION. Australian Journal of Chemistry do not appear to be IF SELECTION = 1 OR 5 PERFORM ACTION-A discounted. ELSE IF SELECTION = 2 OR 3 PERFORM ACTION-B Yours sincerely, ELSE IF SELECTION = 4 OR 7 PERFORM ACTION-C Ian Ross, ELSE PERFORM ACTION-D. Chairman 209. EXIT. This also requires 6 fewer lines of coding and 4 fewer The Editor, paragraph names. Dear Sir, In each case I believe the proposed coding is easier to THE AUSTRALIAN COMPUTER JOURNAL understand. I have read the May 1978 article “Effective Yours faithfully, Structuring of COBOL Programs” by P.L. Juliff with Allan Coote interest and with sympathy for the author’s cause. Senior Lecturer in Accounting, Mr Juliff is to be commended for drawing attention University of Wollongong. (particularly, I hope, the attention of commercial programmers) to the use of the decision-table binary The Editor, approach (1, 2, 4, .. ..) in evaluating multiple conditions. Australian Computer Journal May I suggest, however, that coupling this approach with a GO TO/DEPENDING ON (as in figure 6) may, in fact, have Dear Sir, lessened the impact. In both figures 5 and 6 the use of simple IF/ELSE statements requires less coding and is more Re: ACJ Article and Subsequent easily understood. “Letter to the Editor" Figure 5, for example, could have been coded as I accept the point made by Mr Coote. The use of a follows:— GO TO . .. DEPENDING ON vs a series of nested IFs is, I feel, partly a matter of personal style and partly a function 100-SELECT-PROCESS SECTION of the number of conditions to be evaluated. For example, 100. would it be considered preferable to have used nested IFs in IF code = 1 PERFORM 120-ROUTINE-X Figure 5 if there had been ten valid codes to identify rather ELSE IF code = 3 PERFORM 130-ROUTINE-Y than three, and if each of the eight rules in Figure 6 had ELSE IF code = 6 PERFORM 140-ROUTINE-Z led to a separate action? Apart from the capacity of the ELSE PERFORM 150-ERROR-ROUTINE programmer’s “mental stack” to cope with nested IFs, 109. many COBOL compilers refuse to compile more than a EXIT. small number of such nestings. I feel therefore that the use of a GO TO .. . This requires 6 fewer lines of coding (7 if you count the DEPENDING ON is a more universally useful approach to comment which is no longer needed) and 4 fewer paragraph the implementation of the constructs illustrated. names. Similarly, figure 6 could have been coded as Yours faithfully, follows:— Peter Juliff Forthcoming National and International Events DATE EVENT LOCALE SOURCE 1978 28 August- 1 September 8th Annual Computer Conference Canberra, Australia ACS September Third International Congress on Electronic Information Processing (IKD) Berlin, Germany ACM 4-6 International Conference on Applications of Machine-Aided Image Analysis Oxford, England ACM 4-6 SIMSIG 1978 Simulation Conference Canberra, Australia ACS 4-8 Medical Informatics Europe: First Congress of the European Federation for Medical Informatics Cambridge, UK IFIP The Australian Computer Journal, Vol. 10, No. 3, August, 1978 119 Forthcoming Events DATE EVENT LOCALE 4-8 South East Asia Regional Computer Conference 1978 (SEARCC 78) Manila, The Philippines IFIP 5-7 1978 International Optical Computing Conference London, UK ACM 5-7 COMPCON Fall 1978 Washington, DC, USA ACM 12-14 Computers in Cardiology Stanford, USA ACM 12-15 3rd International Congress on Data Processing West Berlin, Germany IFIP 13-15 Fourth International Conference on Very Large Data Bases West Berlin, Germany ACM 19-22 Conference on Microprocessors in Automation and Communications Canterbury, UK ACM 21-23 International Conference on Interactive Techniques in Computer Aided Design Bologna, Italy ACM 26-29 Fourth International Conference on Communications Kyoto, Japan ACM 27-29 1st Annual Conference on Modular Computers Upton, USA ACM October 2-5 International Symposium on Operating Systems Paris, France ACM 10-12 3rd USA-Japan Computer Conference San Francisco, USA ACM 10-12 Second Conference of the European Co-operation in Informatics Venice, Italy ACM 15-19 American Society for Information Science Annual Meeting New York, USA ACM 25-27 Fourth IEEE Symposium on Computer Arithmetic Santa Monica, USA ACM 29 October- New Orleans 1978 International Data Processing Conference & Business 1 November Exposition New Orleans, USA ACM 5-8 November Second Annual Conference on Computer Applications in Medical Care Washington, DC, USA ACM 7-10 4th International Conference on Pattern Recognition Kyoto, Japan IFIP December 4-6 Winter Simulation Conference Miami Beach, USA ACM 4-6 National Telecommunications Conference Birmingham, USA ACM 4-6 ACM 1978 Washington, USA ACM 5-8 Management and Evaluation of Computer Performance San Francisco, USA ACM 1979 January 15-19 IFIP/IFAC Working Conference on Socio-Technical Aspects of Computerisation Budapest, Hungary IFIP February 20-22 ACM Computer Science Conference Dayton, USA ACM April 23-25 Working Conference on Formal Models and Practical Tools for Information Systems Design London, UK IFIP May 21-23 IFIP/IFAC Conference, PROCLOMAT '19 Michigan, USA IFIP 21-26 Working Conference on “Evaluation of Effectiveness of Medical Action, Methodology and Experiences” Bordeaux, France IFIP 28-31 2nd International Conference on “Tele-Informatics” Paris, France IFIP 31 May- 1 June Working Conference on “The Information Systems Environment” Bonn, FRG IFIP June 4-8 2nd Conference on “Computers and Human Choice” Vienna, Austria IFIP 10-16 2nd IFIP/IFAC Symposium on “Software for Computer Control” Prague, CSSR IFIP 19-21 IFIP/IFAC Workshop “Real-Time Programming” Prague, CSSR IFIP July 16-20 Sixth International Colloquium on Automata, Languages and Programming Graz, Austria ACM 120 The Australian Computer Journal, Vol. 10, No. 3, August, 1978 DRANETZ Power Line Disturbance Analysers When you are concerned with sophisticated electronic equipment you are also concerned with power line quality. The Dranetz Line Disturbance Analyser will deliver the data to enable you to pinpoint the effects of power line anomalies on equipment and to analyse the quality of supply. Single phase, three phase and AC/DC analyser models are available to provide a permanent printed record of each disturbance by time of occurence, magnitude, duration and phase. g.ta CONSIDER THESE FUNCTIONS: • Internal battery provides four hours • Complete round the clock record of operation during power-down time. disturbances. NOW CONSIDER THESE OPTIONS: • Time clock may be set to system or real • Under/over frequency monitoring for time. 50 and 400 Hz. • Switch selectable threshold values for • External event marker. impulse, cycle to cycle changes in • Adaptors to measure impulse area, RMS levels and slow changes in steady polarity of impulse and direction of state RMS levels. impulse. • Measures impulses as fast as 0.5 FEATURES: micro-seconds. • A rugged, portable (6.8 kg) instrument • Internal computer accumulates fitted in weather-proof case. statistical data for daily summary • Easy to connect, easy to read read-out. permanent record for analysis. For further details contact; ELECTRICAL EQUIPMENT LTD. 192 Princes Highway, Arncliffe, N.S.W. 2205. Tel.: 59 0291 8 Remont Court, Cheltenham, Vic. 3192. Tel.: 550 4522 25 Maud Street. Newstead. Q’ld. 4006. Tel.: 52 3962 ANDERSON DIGITAL EQUIPMENT AUSTRALIAN AND NEW ZEALAND DATARAM REPRESENTATIVES FOR DATARAM ANNOUNCES THE AVAILABILITY OF BOTH ADD IN/ADD ON MEMORY FOR: DATA GENERAL VARIAN NOVA ALL MODELS INTERDATA DEC, PDP11, PDP8 D.C.C. FULL SERVICE AND CHANGEOVER FACILITIES FOR THE ADD ON/IN MEMORIES NOW OFFERED IN THE NEWLY EXPANDED FACILITIES OF ANDERSON DIGITAL ELECTRONICS IN MELBOURNE. DEC VARIAN DATA GENERAL INTERDATA PDP-8/A 620/f Nova 1200 Model 50 PDP-8/E 620/i Nova 1210 Model 55 PDP-8/F 620/L Nova 1220 Model 70 PDP-8/M 620/L-100 Nova 1230 Model 74 PDP-11 /03 PDP-11/04 PDP-11/05 622/i Nova 2/4 7/16 PDP-11/10 V-71 Nova 2/10 7/32 PDP-11 /34 PDP-11/35 V-72 Nova 3 8/32 PDP-11 /40 V-73 PDP-11/45 V-74 PDP-11/70 DCC SEE US ON STAND 21 116 ATACS-8 116E IN CANBERRA Anderson Digital Equipment [X l^PE P.O. Box 322, MT. WAVERLEY VICTORIA AUSTRALIA 3149 TELEPHONE: (03) 543 2077 BRSIBANE 59 6436, PERTH 325 5722, CANBERRA 58 1811, ADELAIDE 79 9211, HOBART 34 4522, DARWIN 8 12505, AUCKLAND 87 6570, WELLINGTON 64 4585. Central Data Get into computing the economical, expandable way FEATURES: Signetics 2650 microprocessor based — All processor signals buffered for TTL fan out of 10 Supervisor programme in 1k of PROM 730 bytes of RAM available to the user Provision for 3k of additional PROM on the board Cassette Interface on the board using 1200/2400 Hz Kansas City standard Composite Video output with 16 lines of 80 characters display format Two parallel input ports, and one bit selectable output port s' % Central Data dynamic RAM boards are available The Central Data System Board with 16k, 24k, or 32k bytes of memory. CDSYSBDA facilitates the writing of programmes in Hexadecimal with only Central Data software includes an Assembler/Editor the addition of a TV monitor, ASCII and an 8k BASIC tape. A Debugger, 12k BASIC and Keyboard and power supply. Assembly Language Package is coming soon. The System Board can be expanded by Other hardware now available and on the way connecting the S-100 Board CDS100BDA. includes Central Data Computer Mainframe with This allows you to plug in any S-100 r SEE US ^ Power Supply, ASCII keyboard with solid-state static memory board with an access time AT low-profile keyswitehes and +5 volt operation of less than 500ns or the Central Data and Floppy Disc controller with one, two or dynamic RAM boards CDXXKBDA. COMPUTER three drives. FAIR 78 For general and specific information: CANBERRA TECNICO ELECTRONICS We are exhibiting at the Australian Computer Conference Fair stands 24, 25 and 26 in the Albert Hall, Canberra from 28th August to 1st September, 1978. Premier Street, Marrickville, N.S.W. 2204. Tel. 55 0411. 2 High Street, Northcote, Vic. 3070. Tel. 489 9322. MO808/778 viii The Australian Computer Journal, Vol. 10, No. 3, August, 1978 (Continued from page vi) wlmM. \\v^ivvvvw designed for dedicated transaction processing, hence avoiding adaptation of standard operating mainframe systems. In addition, TRAX uses standard ANSI ’74, COBOL or BASIC-Plus 2 and a simple forms language to allow use by operators unaccustomed to handling computers. Diagrammatic illustration of the Mul-T-Lock system. The central The system is multi-terminal, featuring the most lock throws steel bolts into the top, bottom and sides of the door advanced application development tools and data frame. safeguards in the computer industry. It can reduce application development time in many instances by more egress of the bolts through the door edges. than 50 percent of that of most mainframe systems. The system is so effective that it is virtually necessary TRAX is designed to manage the collection, to demolish the door to force an entry. organization, storage and retrieval of business transaction The “Mul-T-Lock” system is distributed by Pita Pty. information for financial institutions, insurance companies, Ltd., Haberfield, N.S.W. government agencies, manufacturers and other commercial TEKTRONIX AT THE ACS-8 COMPUTER and industrial users. CONFERENCE SECURITY LOCK SYSTEM Tektronix Australia Pty Limited will exhibit their A security lock system based on the bank vault door range of Computer Graphic Products at the ACS-8 Con principle is now available for office use. ference, Canberra, 28 August-1 September. The system, called “Mul-T-Lock”, was recently tested Tektronix are solution specialists. Their line of by the Melbourne testing authority, Technisearch Limited, graphic terminals are used to support all kinds of who said in their report, “The test was stopped after one applications in science, industry, government, business and million cycles were completed. No failures or malfunctions education. The product range includes the 4051 intelligent were observed”. Computer Graphic System that decreases dependency on The lock operates on an eccentric cam principle, central computers. The versatile 4006-1 terminal that brings pushing steel rods into the door frame at top and sides and graphics within the price of alphanumerics. The 4020 series the doorstep at the bottom, at the turn of the Yale-type of refreshed terminals which offer the user flexibility, from key. alphanumerics through form-filling to graphics. These rods, which penetrate 20 mm into the frames The Tektronix 4010 series of high resolution Graphic when in the locked position, all act independently of each Terminals, from the 11-inch 4010 to the 19-inch 4014, are other, so that breaking one to force an entry leaves the used widely in all types of interactive graphic applications. three others undisturbed. In addition to this the versatile 4662 B-size Digital Plotter, The lock itself is protected by steel plates on both Interactive Graphics Software Packages, plus a series of outside and inside of the door, solidly anchored with peripheral units including discs, file managers, hard-copy telescopic bolts. Steel plates also protect the points of devices, digitizers and tape drives, combining to form a The Australian Computer Journal, Vol. 10, No. 3, August, 1978 ix Announcing a brilliant concept in terminals. Model 43 Buffered ASR with paper tape. High transmission speeds • Powerful character-oriented editing •'Solid state buffer storage • 8-level paper tape punch and reader •Simultaneously local/on-line operation • Full forms control • 80 or 132 print positions • Multiple copies • Numeric keypad • Multi-point capability. Teletype* Model 43 Buffered Series- designed for maximum terminal utilization. The Teletype* extended buffer will provide When the printer is not occupied with message up to 20,000 characters of storage for sending, preparation, it can print sent and received receiving and editing. These terminals can messages. Result: maximum utilization. Initially automatically send and receive on-line via the available in buffered KSR (4K), it will also be buffer at 10 or 180 cps while, at the same time, available in buffered ASR with paper tape and messages can be edited and prepared. This buffered R.O. configurations at a later date. capability enables the operator to keyboard Teletype* Model 42 Buffered Series continuously, yet always keep the terminal A new 5-level concept particularly attractive available to receive messages. for international Telex tape preparation. For further details please complete and mail the coupon. STC DATA COMMUNICATIONS I Moorebank Ave., Liverpool, N.S.W. 2170 'Registered trade mark Teletype Corp. I I would like to know more about Teletype* Model 43 I I Teletype* Model 42 !□ Buffered Series |__ | Buffered Series DATA COMMUNICATIONS STC 1° Teletype* Model 43 Series NAME:. Standard Telephones and Cables Pty. Limited: Sydney 602 0333; Canberra 959883; Brisbane, Fred Hoe I ADDRESS: Melbourne 4801255; Launceston 263939; and Sons 2774311 ; Adelaide 425671; Port Moresby 256933; Perth, M.J. Bateman 4447788. L- -POSTCODE: U502 product range that makes Tektronix the Graphics Leader. transmission. The range of products above will be on show at Buffered ASR terminals also include paper tape ACS-8. facilities. In conjunction with ACS-8 Tektronix Australia has Editing capabilities permit any text to be located by announced several new Computer Graphic Products. They string searching, quickly retrieved and changed by character include a Colour Graphics Terminal, a 25-inch Graphic deletion and insertion. Terminal, a C-size Programmable Plotter, and a new library The model 42, a new 5-level family of terminals based of Graphics Software. These products were previewed at on the proven quality of the model 43 line that provides the NCC in the United States in June. Full world-wide both sold-state buffering and paper tape option for unique product release, including Australia, is targeted for late efficiency and flexibility in message communications' 1978. systems. The 5-level code configuration conforms with the NEW TELETYPE TERMINALS LAUNCHED CCITT No. 2 standard making the model 42 line S.T.C. has announced a number of new terminals and particularly attractive for international Telex tape enhanced terminal features that significantly expand its preparation. existing line of message communications data equipment. IT PAYS TO ADVERTISE! In the May 1978 issue of the ACS Journal, Cemac Interiors advertised a recently completed job in Canberra. It involved full and half height partitions and access flooring for the TAB. Flooring offered the best value: SSBpa*' A! (he new TAB Computer C*nlr« In Conbwo, Iwo Unlvoe 9400’s, IMonoger.ACT.TA8. five IntetdoW 7/32’s end two Dtoiiof Equipment POP 81 systems wifi soon be imtolW. Throughout me vast IBUm5 Root area, consisting of three i offers tour panel: compete levels. Cemoe Tote i ond task Access floors we selected lor the lighting, contact Cemoe Interiors. carpeted computer room, me corpeted telephone belting centre, and tor the ground floor computer Brochures ond details from Cemoe Interiors: ond technical repair oreo, white [cemac rrceirr e»3i« u»«m high pressure laminate tiles we unSOUftHC...... Q AMlAiK dMM ISS&UI£-...... ISC7811 HC WT...... "Cemoe fate ottered on WSCItSA..8 .. 22 89 FfRTH....6 ( 3(1682 orSl-sWie cospe! conymg ofrre 823706 4(7863 Early June saw an enquiry received from a prospective client who had read the ad. He noted Cemac The new Teletype TM terminals include the model 43 also handled other products and appeared knowledgable in — a growing, versatile family of 8-level message terminals the computer environment field. capable of interactive and batch communications. After an initial telephone conversation a meeting was The terminals are configured in receive/only, arranged. Four days later not only had a new computer keyboard send/receive and automatic send/receive versions. room been discussed, the site visited (a little used W’house), Other new features include friction and pinfeed brief been given but a room had been designed, costed and matrix printers that operate at 10 or 30 characters per scheduled, and a quotation was in the clients hands! second. With the end of the financial year and the end of the Either half/full-duplex mode, prints up/low ASCII Federal governments 40 percent investment allowance characters, and features automatic paper tape reader/punch rapidly approaching a decision had to be made quickly. control plus answer back. Senior level meetings were arranged and executed. By the Choice of interfaces are available including EIA June 30th deadline, Cemac Interiors had been (RS232C) (20 to 60 ma). commissioned to create a complete computer environment Buffered model 43 terminals are offered for involving partitions, ceilings, access flooring, air point-to-point and multi-point message communications. conditioning, smoke detection, inert gas fire protection and The buffer provides up to 20,000 characters of storage for electrical installation. sending, receiving and editing. Cemac had another name to add to its ever These terminals can automatically send and receive lengthening list of clients, that of Capitol Motors. on-line via the buffer at 10 to 180 cps while messages are How long now before we see an ad featuring the simultaneously being edited and prepared for future Capitol Motors Installation. The Australian Computer Journal, Vol. 10, No. 3, August, 1978 xi **l SEMITE BEST**“I’m Clive Bendun, Marketing Manager for ADDS screens. I know my product, and I know my competition. And I know which one I’d rather be selling. You see, the other screens make the same basic mistake. They give you some of the features, then tty to make up the difference in options. Only ADDS give you all the features included in the price. For instance, on ADDS Regent we give you visual highlighting, line drawing, extensive formatting, self diagnostics, upper and lower case, numeric pad and a status line. All that, at a price no-one else can match. Call me now for an ADDS demonstration. At your office or mine.” Melbourne: 03-2674388 ' Sydney: 02-9223100 Brisbane: 07-364799 HR<5 -: ... - (Canberra: 062-806573 maMwi i Adelaide: 08- 2723588 Perth: 09- 3217264 warn Auckland: 09-778543 Wm SIGMA DA1A CORPORATION phg29so The Australian Computer Journal, Vol. 10, No. 3, August, 1978 IFIP Publications available at 15% discount ISSUE OF THE AUSTRALIAN COMPUTER JOURNAL, AUGUST, 1978 Please fill in the order form on the back of this brochure and return it with payment directly to D.A. BOOK DEPOT PTY. LTD. 11-13 Station Street, Mitcham, Vic. 3132. Phone 873 2825, 873 2826 Cited from DATAMATION, September 1977: Informal Introduction Communicate all implications to ALGOL 68 ... five panel sessions around the so cial impact of computers and infor by C. H. LINDSEY, University of Man mation processing .,. chester and S. G. VAN DER MEULEN, ... Another welcome addition was the University of Utrecht. plethora of sessions devoted to busi ness applications and administration. Revised edition 1977 370 pages The IFIP program committee carefully Paperback ISBN 0-7204-0726-5 targeted these discussions at dp man List price paperbackA$ U oQ agers, bringing together big names in international computing to talk on Discount price paperback: ^-| -j such topics as data base manage ment, distributed processing, micro Hardbound ISBN 0-7204-0504-1 processors, telecommunications and Hardbound list price: A$28 00 programming. / Dfl. 70.00 Hardbound discount price: A$23.80 CONTENTS: The following key papers are included: Fault-Tolerant Computing (Algir- This completely revised edition of the das Avizienis, U.S.A.). Semantics and the Informal Introduction is based on the Foundations of Program Proving (J. W. De Revised Report of the Algorithmic Information Bakker, The Netherlands). Perspectives Language ALGOL 68. Processing 77 and Networks: Past, Present and Future The Language ALGOL 68 was design (P. Baran, U.S.A.). Molecular Graphics - ed by an IFIP Working Group and for The Computer Scientist as ’’Toolsmith” (F. Proceedings of the IFIP Congress '77, mally defined in a Report in 1969. Toronto, Canada, August 8-12,1977 P. Brooks, U.S.A.). Economics of Informa tion Processing in Distributed Systems (J. Since that time the language, in whole edited by BRUCE GILCHRIST, Colum C. Emery, U.S.A.). Computer-Aided Circuit or in part, has been implemented on a bia University, New York. Design (M. A. Gavrilov, U.S.S.R.). Impact of variety of computers and substantial Data Base Technology on Business Sys experience has been gained by its IFIP CONGRESS SERIES, Volume 7 tem Design (J. A. Gosden, U.S.A.). Trends use. One leading computer manufac and Developments in CAD (J. Hatvany, turer has released an implementation 1977 xxvi + 998 pages Hungary). Trends in Computerized Educa ISBN 0-7204-0755-9 tion Systems (J. Hebenstreit, France). in virtually complete agreement with the current official definition, and it List price: A$70.00 Education in Computing Versus User should only be a matter of time be Dfl. 175.00 Needs (J. N. P. Hume, Canada). Process Control with Faulty Information (N. N. fore others follow. The experience of Discount price: A$59.50 Krassovsky, U.S.S.R.). Education in Com implementation and use lead to many puting - Impact on Scientific Applications proposals for changes to the lan With its focus on the congress theme (B. Levrat, Switzerland). Numerical Methods guage, which are now incorporated in of “The Maturing Profession-Perspec for Variational Inequalities - Applications in Physics and in Control Theory (J. L. the Revised Report - the official, ri- tives and Prospects”, this volume of Lions, France). Program Verification and gourous and final definition of the proceedings will cater for the individ Verification Oriented Programming (D. C. machine independent programming ual interests of specialists in a very Luckham, U.S.A.). A Portable Operating language ALGOL 68. broad range of fields associated with System (D. Morris, U.K.). On Being Creative This new edition should prove an computing. In addition, it provides a in CAD (N. Negroponte, U.S.A.). Architect- indispensable tool for all users of comprehensive survey of the most ture of Next Generation of Data Manage ALGOL 68; it could also serve as a topical developments in information ment Systems (G. M. Nijssen). Formaliza tion of Concurrent Processes (Toshio text in courses on advanced machine processing, a survey invaluable for Nishimura, Japan). Using Precise Spec independent programming languages, those who need to keep up to date ifications in the Development of Software as well as a valuable reference sour with the subject’s many facets. The (D. Parnas, Federal Republic of Germany). ce. 1977 Congress, like its predecessors, Packet Networks: Issues and Choices (L. brought together a group of the world’s Pouzin, France). The Future Potentials of “Consequently this is a work that foremost computer science authorities, Packet Switching (L. Roberts, U.S.A.). Suc should be in every computer li and a special effort was made by these cessful Approach to the Management of brary, and that will be invaluable Change (M. Roark, U.S.A.). Impact of In experts to ensure the particular rel to anyone involved with a real un formation Systems on Organizational evance of the conference program to Thinking (R. I. Tricker, U.K.). Beyond To derstanding of what computing in business users of computers. day’s Computers (M. V. Wilkes, U.K.). volves." The Computer Journal bases, the need for improved hard ing Languages - The Future of Pro Architecture and ware and software technology for build gramming?” was organized. A tran Models in Data Base ing, managing and using these data script of this well attended event has bases is becoming increasingly im been included in this book. Management Systems portant. This need is particularly acute The scope of the papers presented in a complex society where the multi and the expertise of the authors, who Proceedings of the Fourth IFIP, TC-2 tude and variety of interrelationships are all personally involved in the ac Working Conference on Modelling in need to be identified, represented, ex tivities and research described, ren Data Base Management Systems, plored, explained and improved. The ders this book of interest to an au Nice, January 3-7, 1977 information covering these relation dience far larger than that assembled ships that is necessary as basis for in the meeting, rooms of the conferen edited by G. M. NIJSSEN, Control Data sound decisions, grows more complex ce. Europe, Brussels, Belgium. in nature and becomes more numer ous in size. Furthermore, the increas CONTENTS: Editor’s Preface. 1. Computer 1977 viii + 326 pages ing on-line use of computer systems Networks, Contributors; G. N. Lance, L. ISBN 0-7204-0758-3 and the emerging development of Pouzin, F. B. Ryan and L. H.- Williams. 2. Computers and Universities, Contribu List price: A$30.00 largescale storage devices (1012 ~ tors: W. F. Atchison, N. V. Findter, H. Dfl. 75.00 1015 bits) suggests that a large share Heinold, H. Jungdaussen, P. Mertens, J. Discount price: A$25.50 of future computer systems will be Nievergelt and K. L. Zinn. 3. Computer oriented towards the management of Oriented Linguistics, Contributors, J. S. very large data bases. Bidn, L. Bole, S. Braun, P. Deussen, R. H. Hartenstein, R. Jakubowski, A. S. Narin'- The study of data base management These proceedings touch on several yani and S. Szpakowicz. 4,. Software, Con systems (DBMS) is gradually being ap tributors; J. J. Arsac, M. L. Coleman, W. current issues in the design, imple Cowell, A. P. Ershov, V. E. Kotov, A. Ma- proached from a more fundamental mentation and use of management standpoint. That is, the conceptual zurkiewicz and D. Schubert. 5. Applications, systems for data bases of up to sev Contributors; L. Borman, A. Finerman, A. foundations of this field are receiving eral hundred million characters. A- Kisiel, B. Mittman, H, Stahn, R. Stamper, considerable attention. The better in mong these are modern trends in E. Straub and M. Uretsky. Panel Session. sight gained in recent years into the data base system architecture, user The Future of Programming Languages - problems encountered in data base language interfaces for defining var The Future of Programming. List of Com management has led to the develop ious data base structures and for re munications Presented at Ad-hoc Sessions. ment of three principal schematic trieving the data on the basis of com designs (“architectures”) for a DBMS, plex queries, techniques for perfor in which the conceptual scheme itself mance improvements, data communi Minicomputer plays the essential role. cation and conversion between differ Software ent data base management systems, At present, there is an on-going pro and tools for application support. Proceedings of the IFIP Conference fessional debate, sometimes referred on Software for Minicomputers, Lake to as the Second Great Debate, on Balaton, Hungary, September 8-12, which of these schemata is to be pre 1975 ferred. These proceedings of the Selected Topics in fourth annual IFIP TC-2 Working Con Information edited by J. R. BELL and C. G. BELL, ference represent the latest contribu Digital Equipment Corporation, May tions of professionals to this debate nard, Mass., U.S.A. on the conceptual schemata in partic Processing IFIP- ular, and the fundamental aspects of INFOPOL-1976 1976 xiv + 334 pages DBMS in general. Various data models ISBN 0-7204-0437-1 are subjected to a penetrating com Proceedings of the International IFIP List price: A$30.00 parative analysis, and the use of /INFOPOL Conference, Warsaw, Dfl. 75.00 natural language in relational data March 1976 Discount price: bases is considered, as is the temporal A$25.50 dimension in information modeling. edited by JAN MADEY, University of Warsaw, Institute of Informatics, War Minicomputers are the most rapidly saw, Poland. proliferating types of computing Systems for equipment and minicomputer soft 1977 xiv + 534 pages ware is the key to success in applying Large Data Bases ISBN 0-7204-0555-6 minicomputers. This book contains List price: A$50.00 the proceedings of the first IFIP work Proceedings of the 2nd International Dfl. 125.00 ing conference to focus on this in Conference on Very Large Data Ba Discount price: A$42.50 creasingly important subject. Eight ses, Brussels, Belgium, 8-10 Septem papers, by leading experts, provide a ber, 1976 wealth of information on the design The International Conference on In and application of minicomputer soft edited by P. C. LOCKEMANN, Univer formation Processing IFIP-INFOPOL- ware while in-depth panel discussions sity of Karlsruhe, Germany, and E. J. 76 was the first of the new format offer a stimulating interchange of NEUHOLD, University of Stuttgart, regional IFIP conferences. viewpoints and insights by teachers, Germany. International experts, selected by the users and software designers. International Programme Committee, Each section of the book is self-con 1976 Second printing 1978 x + 224 pages presented survey-type papers to an tained so the reader may concentrate ISBN 0-7204-0463-0 audience of over four hundred, the on those parts of direct interest and List price: A$24.00 majority being computer specialists value to himself. Dfl. 60.00 from the host country. Discount price. A$20.40 The papers covered a variety of topic "Every professional man will certainly al subjects which included Computer find this book of great interest be Networks, Computers and Universi cause it gives a stimulating idea on Because record-keeping and decision ties, Computer Oriented Linguistics, what the clever imagination of pro making in industry and government Software and Applications. On the grammers can achieve with limited are based largely on information last day of the conference, a panel hardware. stored in computer-processable data session on "The Future of Programm IAG Communications in June 1976. Specialists in the field Modelling in Data from 12 different countries attended Computer Base Management the conference. Performance The papers in' this volume describe Systems advances which have been made since IFIP Working Group 7.3 on Computer the PROLAMAT 73 conference was System Modelling Proceedings of the IFIP, TC-2 Working held. The fields covered include pro Conference, Freudenstadt, Germany, gramming for numerical control, inte edited by MANI K. CHANDY, Univer January 1976 grated CAD/CAM systems, manufac sity of Texas, Computer Science Dept., turing systems, computer aids to work Austin, Texas, and MARTIN REISER, edited by G. M. NIJSSEN, Control Da shop planning and computing tech Thomas J. Watson Research Center, ta Europe, Brussels, Belgium. niques as applied to CAD and CAM. Yorktown Heights, New York. This volume thus represents a record 1976 Second Printing 1978 of the current state-of-the-art, discus 1978 xiv + 546 pages viii + 418 pages sing developments in both academic ISBN 0-444-85038-4 ISBN 0-7204-0459-2 institutions and industry. No compar List price- A$48.00 List price: A$36.00 able work is available. Dfl. 120.00 Dfl. 90.00 Discount price:AS40.80 Discount price: A$30.60 The area of central computer and Some sixty top-ranking EDP profes Education and Large computer communication system an sionals; users, implementors, research alysis has come a long way from the workers and vendors were specially Information Systems early attempts, about a decade ago, invited participants at the IFIP Work to the present state-of-the-art as re ing Conference on Data Base Man edited by RICHARD A. BUCKINGHAM, presented in this volume, the most agement. Their combined efforts have Birkbeck College, London, England. outstanding difference .between this produced a collection of papers deal conference and previous ones lies in ing with fundamental issues of data Proceedings of the IFIP TC3/TC8 its emphasis on case studies and base management and modelling, re Working Conference, April 18-21,1977, careful validation of results. sulting in the most comprehensive The Hague, The Netherlands. The 32 papers presented in this book work of its kind ever published. give what is perhaps the most up-to- These preceedings, crucially impor 1977 xvi + 230 pages date survey available on current tant to the practice of Data Base Man ISBN 0-444-05047-3 developments in computer system agement Systems - now and in the modelling. As such, it will be wel future, will be of vital interest to any List price: A$26.00 comed by computer scientists and by one participating in design and imple Dfl. 65.00 those concerned with the applications mentation of an efficient data base Discount price: A$22.10 of computers in many fields. management system, or in the field of data modelling in general. This work gives a complete descrip tion of an important confrontation "... The papers presented at the Con Formal Descriptions between educators and practitioners ference provide an up-to-date view of in the field of information processing. of Programming many of the debates within and among It discerns three essential require the different approaches to data base ments for the successful development Languages management" of any informations system: the com The Computer Journal Proceedings of the Working Conferen bination of both theoretical training ce on August 1-5, 1977, St. Andrews, and practical experience for those in N.B., Canada volved in actual design activity; the suitable blend of techniques derived Organized by Technical Committee 2: Advances in from different disciplines; and the ap Programming: International Federation preciation of potential opportunities for Information Processing Computer and problems for members of the or ganization within which the design edited by ERICH J. NEUHOLD, IBM Aided Manufacture takes place. Thomas J. Watson Research Center, An important assumption of the con Yorktown Heights, New York State, edited by D. MCPHERSON, Computer tributors of the papers published here, U.S.A. Aided Manufacture Division, National is that practical and useful results in Engineering Laboratory, Glasgow, this area can only be obtained by the 1978 about 700 pages Scotland. participation of practitioners. ISBN 0-444-85107-0 It is not surprising that the wide vari List price:A$60.00 Proceedings of the Third International ety and spread of "small" information Dfl. 150.00 IFIP/IFAC Conference on Programming systems and the involvement of per Discount price.'A$51 ,00 Languages for Machine Tools, PROLA- sonnel other than project team mem MAT76, Stirling, Scotland, June 15-18, bers emerge as important issues. 1976. These proceedings also clearly show This proceedings- volume contains a that large, complex information sys stimulating collection of 26 excellent 1977 ix +468 pages tems are rapidly becoming an integral papers, surveys and reports. The pa ISBN 0-7204-0500-9 component of organizational efficien pers were presented at the Working List price: A$44.00 cy and effectiveness. The recommen Conference on the Formal Description Dfl. 110.00 dations of the conference reached by of Programming Concepts held in Discount price: A$37.40 consensus (and included in this vol Canada in 1977. Experts in the field ume) form an important landmark in from 18 different countries attended the maturing of the information pro the conference, the aim of which was This book contains the full texts of the cessing profession. Carefully edited "to explicate programming concepts 35 papers presented at the PROLAMAT discussions are a considerable asset through the development, examina 76 Conference on Computer Aids to to the relevance and usefulness of tion, and comparison of various formal Manufacture, held in Stirling, Scotland, this work. models of these concepts”. •: • AIMS OF THE JOURNAL PAPERS PUBLISHED This journal serves managers, profes Vol. 1, no. 1 sionals, data base administrators and A Forecast of the Future of Computation senior executives of organizations (C. Hammer, USA) Marketing the MIS (C. D. Schewe, J. L. which design, implement and manage Wiek and R. T. Dann, USA) Information Systems Applications. The A Prototype Approach to Information Sys major aims are: tem Design and Development (L. Bally, •To collect and disseminate informa Germany; J. Brittan, United Kingdom and tion on new and advanced develop K. H. Wagner, Germany) ments in the field of applied infor An Inter-Related Processing Network mation systems; Architecture (C. Houen, Canada) An Investigation of Information System • To provide material for training and Utilization (S. R. Barkin and G. W. Dickson, education in administrative data USA) systems; Vol. 1, no. 2 • To encourage further progress in Organizational Structure of a Complex information system methodology Data Processing Department (N. Ahituv and and applications; M. Hadass, Israel) • To cover the range of information Information for Strategic Planning - An Analysis (W. E. King, USA) system development and usage in A Conceptual Model of an Interfunctional their use for managerial policies, Data Base System (Z. Ryznar, Poland) The International Journal of strategies, and activities for busi An Inter-Related Processing Network Ar Management Processes and ness, public administration, and in chitecture - Part II (C. Houen, Canada) ternational organizations; Systems • To act as the formal publishing me SUBSCRIPTION dium for IAG: The IFIP Applied In Chairman of the Editorial Board: INFORMATION formation Processing Group in its Information & Management is published PROFESSOR E.H. SIBLEY scientific and educational role. in volumes of 6 issues; one volume per Department of Information Systems year (approx 360/400 pages). The first Management, University of Maryland, issue appeared in October 1977. College Park, MD. 20742 USA The subscription price for libraries will or amount to/\$46.00/ Dfl. 115.00. IAG Headquarters, FREE SPECIMEN COPIES For individual professionals: A$24.00? 40 Paulus Potterstraat, ARE AVAILABLE FROM Dfl. 60.00 (prices mentioned are in Amsterdam, The Netherlands D.A. BOOK DEPOT PTY. 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MELBOURNE 654 4044 SYDNEY 231 6877 BRISBANE 221 1855 PERTH 3222488 ADELAIDE 2721144 CHRISTCHURCH 799 060 WELLINGTON 739 133 AUCKLAND 797079 i^KEY PERSONNEL THE AUSTRALIAN COMPUTER JOURNAL Price: $3.50 per copy to non-members. $1.50 per copy to members. Volume 10, Number 3 AUGUST, 1978 The Australian Computer Journal is an official publication of the Australian Computer Society Incorporated. Contents: Subscription and orders should be sent to PO Box 640, Crows Next, 2065. Office-Bearers 82-86 Software Physics and Program Analysis President: A.R. BENSON D.J.J. van der KN1JFF Vice-President: A.H.J. SALE Immediate Past President: R.S. NORTHCOTE 87-97 Is Disciplined Programming Transferable, National Treasurer: V.G. WHITELEY and is it Insightful? National Secretary: G.K. PIRIE CHARLES LAKOS and ARTHUR SALE Chief Executive Officer: R.W. RUTLEDGE P.O. Box 640, CROWS NEXT, N.S.W. 2065 98-101 Part Management in the CYBER76-CSIRONET Telephone: 929.2219 Interface Editorial Committee: B.J. AUSTIN Editor: A.Y. MONTGOMERY Department of Computer Science, 102-114 A SNOBOL 4 Program to Clean Up Monash University, Clayton, Victoria. 3168 FORTRAN Source Associate Editors: JOHN D. BLACKBURN J.M. BENNETT, G.N. LANCE, 115-117 A Criterion for Determining the Number T. PEARCEY, P.C. POOLE of Groups in a Classification D.A. RATKOWSKY and G.N. LANCE Published by: Associated Business Publications, 28 Chippen Street, Chippendale, N.S.W. 2008. Tel. 699-5601, 699-1154. Represented by: Queensland: Beale Media Services, 232 St. Paul’s Terrace, Fortitude Valley, Brisbane. Phone 52-5827. Special Features: Victoria and South Australia: Derrick, Lewis & Associates, Ashley House, 409 St Kilda Road, Melbourne 3004. Phone 267-4022. U.S.A.: International Newspaper and 86,114 Book Reviews Trade Advertising, 1560 Broadway, New York, 36. 101 An Overview of Programming Practices Italy: Publicitas, Via E. Filiberto 4, Milan. - Appendix A, Appendix B France: Gustav Elm, 41 Avenue J.M. YOHE Montaigne, Paris 8. Advertising inquiries should be referred 118-119 Letters to the Editor to one of the above addresses. Printed by: 119 Forthcoming National and International Events Publicity Press Ltd., 29-31 Meagher Street, Chippendale, N.S.W. 2008. SUBSCRIPTIONS: The annual subscription is $10.00. All REPRINTS: 50 copies of reprints will be provided to authors. subscriptions to the Journal are payable in advance and should be Additional reprints can be obtained, according to the scale of sent (in Australian currency) to the Australian Computer Society charges supplied by the publishers with proofs. Reprints of Inc., P.O. Box 640, Crows Nest, N.S.W. 2065. individual papers may be purchased for 50 cents each from the PRICE TO NON-MEMBERS: There are now 4 issues per annum. Printers (Publicity Press). The price of individual copies of back issues still available is $1.50. PAPERS: Papers should be submitted to the Editor, authors should Some are already out of print. Issues for the current year are consult the notes published in Volume 9, pp. 45-49 (or request a available at $3.50 per copy. All of these may be obtained from the copy from the National Secretariat). National Secretariat, P.O. Box 640, Crows Nest, N.S.W. 2065. No trade discounts are given, and agents should recover their own MEMBERSHIP: Membership of the Society is via a Branch. handling charges. Special rates apply to members of other Computer Branches are autonomous in local matters, and may charge different Societies and applications should be made to the Society concerned. membership subscriptions. Information may be obtained from the following Branch Honorary Secretaries. Canberra: P.O. Box 446, MEMBERS: The current issue of the Journal is supplied to personal Canberra City, A.C.T. 2601. N.S.W.: P.O. Box N250, Grosvenor St, members and to Corresponding Institutions. A member joining Sydney, N.S.W. 2000. Qld: Box 1484, G.P.O., Brisbane, Qld. 4001. part-way through a calendar year is entitled to receive one copy of S.A.: Box 2423, G.P.O., Adelaide, S.A. 5001. W.A.: Box F320, each issue of the Journal published earlier in that calendar year. G.P.O. Perth, W.A. 6001. Vic.: P.O. Box 98, Fast Melbourne, Vic. Back numbers are supplied to members while supplies last, for a 3002. Tas.: P.O. Box 216, Sandy Bay, Tas. 7005. charge of $1.50 per copy. To ensure receipt of all issues, members should advise the Branch Honorary Secretary concerned, or the National Secretariat, promptly of any change of address. Copyright ©1978. Australian Computer Society Inc. The Australian Computer Journal, Vol. 10, No. 3, August, 1978