COMPARISON AND MAPPING OF THE RELATIONAL AND CODASYL DATA MODELS -- AN ANNOTATED BIBLIOGRAPHY

Gary H. Sockut

Institute for Sciences and Technology National Bureau of Standards Washington, DC 20234

Two of the best-known data models are the Computing Surveys, ACM, vol. 8, no. and the CODASYL model ], Mar. 1976, pp. 43-66. (sometimes called the DBTQ, network, or data structure set mode]~ . There have E. F. Codd, "A Relational Model of been many efforts at comparing the two Data For Large Shared Data Banks", mode3s and at defining mappings between Commun. ACM, vol. 13, no. 6, June them. The publications 3isted in this i~, pp. ~77-387. bibliography describe some o~ these efforts and some related topics. I invite For background on the CODASYL model, see readers' suggestions for additional sources such as: entries for possible inclusion in a future bibliography. % omit publications on the CODASYL Data Description Language more general topic of data base Committee, "Journal of Development", conversion. Materiel Data Management Branch, Dept. of Supply and Services, Following each reference, I describe the Canadian Govt., Hull, Que., Canada, publication briefly, usually by quoting Jan. 1978. parts of the author's abstract and/or main text. Often I supplement or replace the C0DASYL author's text with my own words, enclosed Committee, "Data Base Task Group in brackets ([]). I do not guarantee that Report", ACM, Apr. 1971. an author's abstract accurately reflects the content of the publication. R. w. Taylor and R. L. Frank, "CODASYL Data-Base Management I do not evaluate the publications, nor do Systems", Computing Surveys, ACM, I guarantee the truth of their statements. vo]. 8, no. I, Mar. 197~, pp. 67-103. Each publication may reflect its author's opinions. Also, because specifications For background on both models, see sources have evolved over the last ten years, some such as: statements may be out of date. The bibliography reveals that the authors have C. J. Date, An Introduction to not reached consensus on equivalence of Sys'-~ems, 2nd ed~, the models, nor on the models' relative Addison-Wesley, R~ing, MA, 1977. merits, nor on the spelling of "data base". J. Martin, Computer Data-Base Organization, 2n~--e~., Prent~'~6~Ha~[ The mention or lack o~ mention of specific Eng]ewood Cliffs, NJ, 1977. commercial products does not imply endorsement or disapproval by the National I thank John Berg, Joe Collica, Don Bureau of Standards. Deutsch, Dennis Fife, Liz Fong, Len Gallagher, Alan Goldfine, Terry Hardgrave, The reader should have some Familiarity Be1 Leong-Hong, Chuck Sheppard, and Ben with data base management and with the two Shneiderman, whose libraries I raided models. For background on the relational innumerable times while amassing this model, see sources such as: bibliography. Terry Hardgrave and Matt Koll reviewed a draft of this paper. D. D. Chamberlin, "Relational Several authors helped me obtain Data-Base Management Systems", publications.

CONTRIBUTION OF THE NATIONAL BUREAU OF The annotated bibliography follows: Sm~NDARDS. NOT SUBJECT TO COPYRIGHT.

55 - M. Adiba and C. De]obel, "The Problem of system which provides a high level the Cooperation Between Different relational data interface". [One D.B.M.S.", G. M. Nijssen (Ed.~ , section of the paper explains that the Architecture and Models in Data Base interface] "is designed in such a way Management- Systems (Proc. IFIP TC-2 that programs can be written on top of Wor~~---Con~ on Modelling in Data Base it to simulate 'navigation oriented' Management Syst., Jan. 1977), database interfaces". "In general our North-Holland, Amsterdam, Neth., 1977 , pp. strategy will be to represent each 1£5-1~6. record type as a relation and to represent information about ordering "We are investigating here the problem and connections between records in the of the cooperation between several form of explicit fields in the DBM~. This cooperation can take place, corresponding relations". [Another for example, via a computer network. section states that an] "important we address ourselves especially to the access path is a binary link". "Binary description of a globa] view of several links are similar to the notion of an data bases". "We have proposed some owner coupled set with manual mechanisms to transform any program membership found in the DBTG written in terms of the global view in specifications". "The main use of programs which can be executed at the binary links in System R is to connect local data base level". [See also child tuples to a parent based on value (Adiba, De]obeY, and L6onard, 1976) and matches in one or more fields". [See (Aaiba and Portal, Igv~)J. also (Lorie and Ni]sson, 1979)].

M. Adiba, C. De]obe], and M. L6onard, "A Auerbach Information Management Series on Unified Approach for Modelling Data in Data Base Management, "A Taxonomy of Data Logical Data Base Design", G. M. Nijssen Structure Models", written by G. C. (Ed.) , Modelling in Data Base Management Everest, Portfolio 21-03-~I, Auerbach Systems (Proc. TFIP TC-2 Wor~g Conf. on Publishers, Pennsauken, NJ, 1979. Modelling in Data Base Management Syst., ]an. ]97~) , North-Holland, Amsterdam, "This Portfolio presents a more Neth., Iq7~, pp. 311-~38. comprehensive taxonomy of data structures; it describes the basic "Here we examine how ... conversion can types of structures, highlighting their be made (in both ways) between network major characteristics and contrasting and relational concepts, using the them through the use of a common DBTG-CODASML and SOCRATE systems as example". [See also (Everest, 1976)]. examples". [See also (Adiba and Delobel, 1977~ and (Adiba and Portal, Igv~)]. C. W. Bachman, "The Data Structure Set Model", in (Rustin, 1974), pp. 1-10.

M. Adiba and D. Portal, "A Cooperation "The relational debate, as I see it, is System For Heterogeneous Data Base over style in retrieval languages, and Management Systems", Information Syst., style, really, is only one aspect of a Pergamon Press, Oxford, UK, vol. 3, no. 3, data base system". "I accept the 1978, Pp. ~9-215. relational view and the data-structure-set view as being "We propose here a functional fundamentally compatible as they are architecture of a cooperation system applied in practice, and I'd like to For heterogeneous DBMS in a network demonstrate the equivalence between the environment" [The paper assumes] "the two views". existence of different local data bases already in use under DBMSs like IMS, Codasyl-]ike systems, SOCRATE, C. W. Bachman, "The Role re]ationa] systems, etc.". "The Approach to Data Structures", Proc. Intl. cooperation system should be able ... Conf. on Data Bases, Heyden, Lon~, UK, to provide facilities for creating and J~y 198~, pp. 1-18. modifying a global view of these local data bases". [See also (Adiba and "This paper examines the Role data Delobel, ]977) and (Adiba, Delobe], and model as an evolutionary step forward L~onard, 19v6)]. in the sequence of data models" [and compares it with other data models].

M. M. Astrahan et a]., "System R: Relationa] Approach to Database C. W. Bachman, "Trends in Database Management", ACM Trans. on Database Syst., Management -- 1975", Proc. Natl. Computer vo]. 1, no. ~, June ~h"~6, pp. 9~-137. Conf., AFIPS, vol. 44, May 1975, pp. ~-576. "System R is a database management

- 56 - [One section says] "I consider the data transfer, and a global view of relational model and the different data bases in a distributed data-structure-set model essentially system. The author states that with compatible ann subiect to some restrictions upon the relational transformation From one form to the and CODASYL models], "the 'expressive other". "The relational mode] and the" powers' of the models are equivalent". [data independent accessing mode]] [See also (Borkin, 1978)]. "appear to be completely at odds with each other" "By comparison, the data-structure-set mode] seems to be an J. Bradley, "An Extended Owner-Coupled Set effective hybrid between these two Data Model and Predicate Calculus for extremes". Database Management", ACM Trans. on Database Syst., vol. 3, no. 4, Dec. 197~, pp. 385-416. R. Bell and P. M. D. Gray, "Description of Access Paths for Realising Relations from [In this data model,] "the logical view a CODASYL Database", Research Rep. of the data in the database is AUCS/TR-R~I, Dept. of Computing Sci., U. essentially relational but with the of Aberdeen, Aberdeen, UK, Jan. ]98~. superimposition of the owner-coupled set concept". "Extended Bachman "The ... system generates Fortran diagrams in modified form can easily be programs to retrieve data from a used in the design of relational CODASYL database in the form of ". relations". "The system generates an internal description of a relation called a 'traversa]', which includes A. F. Cardenas and M. H. Pirahesh, "Data elements representing both algebraic Base Communication in a Heterogeneous Data operators and CODASYL DML commands". Base Management System Network", Information Syst., Pergamon Press, Oxford, UK, "~'?--~, no. l, 1980, pp. 55-79. H. Biller, "On the Equivalence of Data Base Schemas -- A Semantic Approach to "An architectural approach is outlined Data Translation", Information Syst., ... in which any user in any network Pergamon Press, Oxford, UK, v ol. a, no. I, node can be given an integrated and Iq79, pp. RS-4V. tailored view or schema (e.g. hierarchical, relational), while in "The equivalence of data base states reality the data may reside in one and data base schemas is defined". "It single data base or in physically is shown, how a and separated data bases, managed (LDDL) can be individually by the same type of GDBMS used to construct a correct (e.g. CODASYL, IMS, relational) or by specification of a translation different GDBMS". "The function. Finally, an example of the entity-relationship model is translation of a CODASYL data base fundamentally used for the highly schema to a relational data base schema logical model layers of the integrated is given". system". [See also (Nahouraii, Brooks, and Cardenas, 1976)].

S. A. Borkin, "Data Mode] Equivalence", Proc. 4th Intl. Conf. on Very Large Data G. 4. Champine, "Current Trends in Data ~, r~, ~p. r~v~, ~.-~-~. Base Systems", Computer, IEEE-CS, vol. 12, no. S, May 1979, pp. 27-41. [This paper defines 'data model' and 'data model equiva]ence'. See also [In part of this paper, the author (Borkin, 1979)]. reviews different data models and describes support of multiple models on one architecture]. g. A. Borkin, "Equivalence properties of Semantic Data Models for Database gystems", Ph.D. thesis, Dept. of Elect. P. P.-S. Chen, "The Entity-Relationship gng~n, and Computer Sci., M.I.T., Mode] -- Toward a Unified View of Data", Cambridge, MA, Jan. 1979; Lab. for Proc. [Ist] Intl. Conf. on Very Large Data Computer Sci. Tech. Rep. 206; NTIS Bases, ACM, Sept. 1975, p. 173 (abstract); ADA055386; slightly revised as Data ACM Trans. on Database Syst., vol. I, no. Models: A Semantic Approach for Database ], Mar. 1976, pp. 9-36. Systems, M.I.T. Press, Camb~-dge, MA, 198~. "A data model, called the entity-relationship model, is [This thesis defines equivalence of proposed". [One section of the paper data models. Motivations include describes how] "the entity-relationship multiple data models for one data base, model can be used as a basis for

- 57 - unification of different views of data: "General purpose support for" the , the relational [non-programming] "users entails mode], and the entity set model" provision of an augmented relationally "Possible ways to derive their views of complete retrieval capability without data from the entity-relationship mode] branching, explicit iteration, or are presented". cursors. It is clear how this capability can be realized with the relational approach". "It is not at E. K. Clemons, "Design of a Prototype all clear how the network approach can ANST/SPARC Three-Schema Data Base System", reach this goal, so long as the Proc. Nat]. Computer Conf., AFIPS, vol. principal schema includes owner-coupled ~[~[, June 1979, pp. 689-696. sets 'bearing information essentially' A relational discipline is suggested as "This paper ... describes briefly how a way out for DBTG users". an ANSI/SPARC three-schema data base system prototype could be constructed". "For the internal level we propose that E. K. Conoley, "Use of a Hierarchical Data a CODASYL data base management system Model to Support a Relational Data be employed. The conceptual level will Management System", M.A. thesis, U. of be a relational system". Texas, Austin, TX, Aug. 1977; NTIS ADA047602.

L. Clough, W. D. Haseman, and Y. H. So, [This describes] "a relational "Designing Optimal Data Structures", Proc. interface for implementation as a front Nat]. Computer Conf., AFIPS, vol. 45, June end to a hierarchical data base". 197~, pp. 829-R37. "Relational operations were implemented in terms of the available hierarchical "This paper is concerned with DBMS functions". developing a methodology for designing optimal network data base structures". [Data description begins in the form of C. J. Date, "An Architecture for networks, which are converted into High-Level Language Database Extensions", hierarchies, then into relations, then Proc. ACM-SIGMOD Intl. Conf. on Management into canonical networks, and finally of Data, June 197~, pp. 1@1-122. into opt~ma] networks, based upon] "the set of queries," [using] "an operations "The is provided with the research mode]" [See also (De, ability to handle all three of the Haseman, and Kriebel, 1978) and well-known database structures (Haseman and Whinston, ]Q77)]. (relational, hierarchical, network), in a single integrated set of language extensions". "A database is E. F. Codd, "A Data Base Sublanguage represented, not as some new kind of Founded on the Relational Calculus", Proc. input/output file, but instead simply 1971 ACM-gIGF!DET [SIGMOD] Workshop on as part of the program's directly Data D~c#iption, Access, and Control, addressable storage area" [See also Nov. l~ff, pp. 35"6R; IBM Research Rep. (Date, 1977) and (Date, 1980)]. RJ 89~ ({15716), July 1971.

"Three principal types of language for C. J. Date, An Introduction to Database data base manipulation are identified: Systems, 2nd ed., Addison-Wesley, Reading, the low-level, procedure-oriented MA, 1977, Chap. 25 ("The Three Approaches (typiFied by the CODASYL-proposed DML), Revisited") , pp. 425-461. the intermediate level, algebraic (typiFied by Project MAC MacAIMS [One section of this chapter defines a language), and the high level, language based upon (Date, 1976). In relational calculus-based data another section, the author argues that sub]anguaqe, an example of which is the relational model is simpler, and described". "Arguments are presented has a firmer theoretical base, than the for the superiority of the CODASYL model. See also (Date, 1980)]. calculus-based type of data base subSanquage over the a]gebraic, and for the algebraic over the low-Revel C. J. Date, "An Introduction to the procedural" Unified Database Language (UDL)", Proc. 6th Intl. Conf. on Very Large Data Bases, ACM, Oct. 1980, pp. 15-32. E. F. Codd and C. J. Date, "Interactive Support for Non-: The "The first description of UDL was given Relational an~ Network Approaches", in in" [(Date, 1976)]. "The present paper (Rust~n, !974), pp. ]1-4]; IBM Research provides an informal introduction to Rep. RJ ]4~ (~21~38) , June 1974. the concepts and facilities of UDL as currently defined ..., and thus forms a

- 58 - rep3acement for the original paper". interfaces consisting of the [See also (Date, Iq77%]. relational, network, and hierarchical models".

C..7. Date and E. ~. Codd, "The Relational and Network Approaches: Comparison of the J. Earley, "On the Semantics of Data Application Programming Interfaces", in Structures", R. Rustin (Ed.), Data Base (Rustin, Iq74), pp. 83-I13; IBM Research Systems (Courant Computer Sci. Symp. 6, Rep. RJ 14~l (~]7S6), June 1974. May 1971), Prentice-Hall, Englewood Cliffs, NJ, 1972, pp. 23-32. "The purpose of this paper is to give some comparisons between these two [This paper compares data base usage approaches (primarily from the at] "three levels of description of application programming viewpoint)" data structures": "(i) The "We now present a discussion of what we implementation level or machine level, consiaer to be the relative advantages (2) A logical (semantic) level in which of the relational approach, under the access paths are specified explicitly, fol]owing headings: simplicity, and (3) A logical level in which only uniformity, completeness, data the relationships between data items independence, integrity and security". are specified". [The second level is not specifically CODASYL].

P. De, W. D. Haseman, and C. H. Kriebel, "Toward an Optimal Design of a Network C. P. Earnest, "A Comparison of the Database From Relational Descriptions", Network and Relational Data Structure Operations Research, Operations Research Models", Computer Sciences Corp., E1 $oc. oF ~erica, Baltimore, MD, vol. 26, Segundo, CA, Apr. 1974. no. 5, Sept.-Oct. 1978, pp. e@5-823. "This paper attempts to bring out the "This paper suggests a method for similarities and differences clearly, building up a network database starting by defining and discussing both models from relational descriptions. The on a common basis of terminology". network generated is optima] in terms "Major conclusions are that (i) the two of data item appearances and, given models are in practice not very that, it is also optimal in terms of different, (2) the relational the number of records". "Some of the structures are somewhat simpler than concepts ... are extensions of the networks, but (37 the price for this is ideas" [in (Clough, Haseman, and So, that the network model has more 79~6~ and (Haseman and Whinston, structural power, and more, not less, 1977) ] . data independence than the relational".

S. M. Deen, "A Canonical Schema for a C. P. Earnest, "Selection and Higher Level Generalised Data Mode] With Local Structures in Networks", B. C. M. Douqu~ Interfaces", Computer J., British Computer and G. M. Nijssen (Eds.), Data Base Soc., vol. 23, no. --3, Aug. 198g, pp. Description (Proc. IFIP TC-2 spec-~T ~l-2S~. Working Conf. on Data Base Description, Jan. 1975), North-Holland, Amsterdam, "A global schema is proposed for a Neth., 1975, pp. 215-237. general~sed data base system capable of supporting interfaces to other systems "We have shown how to superimpose -- notably Relational, Codasyl and higher level structures on the records Adabas -- through appropriate local and record interconnections of a schemas and data manipulation database, and how to use these languages. The proposed global schema structures for data selection and consists of entries in the form of manipulation". normalised relations".

R. El-Masri and G. Wiederhold, "Properties A. Dogac and E. A. Ozkarahan, "A of Relationships and their ~eneralized DBMS Implementation on a Representation", Proc. Natl. Computer Database Machine", Proc. ACM-SIGMOD Ig80 Conf., AFIPS, vol. 49, May 1980, pp. Intl. Conf. on Management o~ Data, May 319-326. p~T--l'i~3-r~'~. "" "We examined the semantic properties of "The design and implementation of a a relationship between two entity generalized database management system classes". "We compared six data models based on the RAP database machine is with respect to the choices they offer described" "The E/R mode] is chosen for the representation of as the Meta Data Model (Conceptual relationships". Schema) which generates external model

- 59 - G. C. Everest• "Basic Data Structure R. Gerritsen, "A Preliminary System for Mode]s Exp]ained With a Common Example", the Design of DBTG Data Structures", Proc. Proc. Fifth Texas Conf. on Computing ACM-SIGMOD Inltl. Conf. on Management of ~s., "l~'gfgfrCS,---~. lrg77C~p~. 3gza6 '. Data• May "I~75, p.--16~----~as~ct)-;- ~un. ACM, vol. 18, no. 10, Oct. 1975, "This paper presents a taxonomy of pp. 551-557. basic data structures which cuts through and omits the secondary [This is based upon (Gerritsen, 1975c) . differences to highlight the most See also (Gerritsen, 1975b)]. important logical differences". "The essential characteristics of each of ... six basic data structure models are R. Gerritsen, "The Relational and Network described and each ~s exemplified using Models of Data Bases: Bridging the Gap", a common example". [See also Proc. 2nd USA - Japan Computer Conf., (Auerbach, I9~g)]. AFIPS, Aug. 1975, pp. 347-351. "An attempt is made to lay to rest the E. Fa3kenberg, "Concepts for the question of supremacy of either the Coexistence Approach to Data Base network or the relational model of data Management", E. Morlet and D. Ribbens bases. It is argued that these two (Eds.} , Intl. Computing Symp. 1977, models correspond to two distinct North-Hollan~, Amsterdam, Neth., Ap~] levels of description; a relational or 19~7, pp. 39-5~. non-procedural level and an access path level. Hence, a translation approach "The idea providing coexistence of is suggested whereby relational various data models and data descriptions can be translated to manipulation methods within one data network descriptions". [See also base management system imposes new (Gerritsen, 1975a) and (Gerritsen, requirements on the design of such 1975c)]. systems". "As a common basis for any external or internal interface, the use of a semantically complete and unique R. Gerritsen, "Understanding Data form of data -- the deep structure of Structures", Ph.D. diss., Grad. School of data -- at the central interface is Industrial Admin., Carnegie-Mellon U.• suggested". "Transformations from a Pittsburgh, PA, Feb. 1975; NTIS deep structure into various ADA00R937. semantically equivalent surface structures of data ~ [(CODASYL and [The system described herein] re]at~onal}] "are shown". "generates a DDL description from a set of queries" [expressed in HI-IQ (a not-exactly-relational language), based M. Fleck, "On the Equivalence of Data Base upon] "data relationships implied by Models" Tech Rep. TR 25.14a, IBM the queries". [The system also] Laboratory, Vienna, Austria, July 1975. "translates a query to COBOL procedure augmented by Data Manipulation "The equiva]ence problem between Language". [gee also (Gerritsen, different data models of a data base 1975a) and (Gerritsen, 1975b)]. system is investigated. The notions of data-equivalence and consistency-equivalence are introduced. J. Goldman, "Automated Generation of A specific solution to gain Relational Schemas for CODASYL Databases", consistency-equivalence is proposed Sperry Research Center Rep. SRC-RP-79-13, where the necessary changes of the data Sudbury, MA, Mar. 1979. models are minima]" "This report" [uses] "the relational mode] ... and "A facility which translates CODASYL the Codasyl DBTG model" database schemas into schemas is described". "The derived relational schema preserves the J. P. Fry and E. H. Sibley, "Evolution of information content of the database and Data-Base Management Systems", Computin~ would support high level data Surveys, ACM, vol. R, no. l, Mar. 197g, sublanguage access to the database, pp. 7-42. both retrieval and update". [See also (Zaniolo, 1979a) , (Zaniolo, 1979b) , and [One section briefly describes several (Zaniolo, 1977)]. data mode]s and compares their terminologyJ. D. Goldschmidt and A. Reiter, "An Implementation of FORAL Using IDMS", B. Shneiderman (Ed.% , Databases: Improving Usability and Responsiveness-(Proc. [n{~. Conf. on Da~'~as~: Improving Usability

- 60 and Responsiveness, Aug. 1978), Academic J. Iossiphidis, "A Translator to Convert Press, New York, NY, 1978, pp. iqi-150. the DDL of ERM to the DDL of System 2@00", P. P.-£. Chen (Ed.) , Proc. Intl. Conf. on "PORAL is a non-procedural data Entity-Relationship Approach to Systems specification and manipulation language An~ysls ~n~---F~6rg 5, Dec. T~79, pp. based on binary associations. IDMS is ~50-57~; later published as a commercial database management system Entity-Relationship Approach to Systems based on a 'network' model and Analysis and Design, North-Holland, belonging to the CODASYL DBTG group of languages. We describe an implementation of a subset of the FORAL "This paper describes ERL a over existing IDM£ nonprocedural data definition language databases". (DDL) for the entity relationship model (ERM) of a data base management system. Also described is the translator built W. T. Hardqrave and E. H. Sibley, "Data to convert ERL programs into the DDL of Model Processing: An Approach to SYSTEM 2~0" Standardization of Database Management Systems", Tech. Rep. 45, Dept. of Info. Syst. Management, U. of Maryland, College H. R. Johnson and J. A. Larson, "Data Park, MD, July 1979. Management for Microcomputers", Proc. COMPCON Fall 79, IEEE-CS, Sept. 1979, pp. "This paper outlines a general 191-194. philosophy and framework for the specification of a data model. [This is similar to (Johnson, Larson, Extracts from scenarios that have been and Lawrence, 1979). See also developed for specification of several (Johnson, Larson, and Lawrence, 1978) well-known data models (e.g., DBTG, and (Larson, Johnson, and Lawrence, relational, TDMS~ are given and 1978)]. discussed" "The scenarios are intended for implementation of an augmented positional processor that H. R. Johnson, J. A. Larson, and J. D. will be able to support different data Lawrence, "Network and Relational models". [See also (Rothnie and Modelling in a Common Data Base Hardgrave, 1976)]. Architecture Environment", Sperry Univac Research Rep. TMA~720, Roseville, MN, Mar. 1979. W. D. Haseman and A. B. Whinston, Introduction to Data Management, Richard "A common data base architecture and ~-rwln,~me~odT--TL, I~77, Chap. 15 its applications in supporting various {"Designing Optimal Data Structures"~ , pp. language file systems and data base management systems are described". "Data base management specifications of [mhis is similar to (Clouqh, Haseman, 197£ CODASYL Journals of Development and So, 1976). See also (De, Haseman, and of SEQUEL 2 are extended". and Mriebe], 197£%]. "Information preserving transformations between submodels within and across the models are specified". [See also B. C. Housel, "QUEST: A High-Level Data (Johnson and Larson, 1979), (Johnson, Manipulation Language for Network, Larson, and Lawrence, 1978), and Rierarchical, and Relational Databases", (Larson, Johnson, and Lawrence, 1978)]. IBM Research Rep. RJ 25£8 {~348£), July 19"79. H. R. Johnson, J. A. Larson, and J. D. "This paper describes a query language, Lawrence, "Transformations Between Network QUEST, which provides a single and Relational Data Models", Sperry Univac interface to the three major data Research Rep. TMA00729, Roseville, MN, models. The initial development was Mar. 1978. aimed at providing a simple but powerful high-level interface for [This paper describes algorithms for network databases. Subsequently, translation (in both directions) however, it Proved straightforward to between "minimally keyed" network extend the semantics in a consistent schemas and "fully keyed" network way to include the hierarchical and schemas, and between fully keyed relational models". network schemas and relational schemas. See also (Johnson and Larson, 1979), (Johnson, Larson, and Lawrence, 1979), and (Larson, Johnson, and Lawrence, 197R)].

- 61 - L. A. Ka] inichenko, "Data Models S. R. Kimbleton and P. S.-C. Wang, Transformation Method Based on Axiomatic "Applications and Protocols", to appear in Data Model Extension", Proc. 4th Intl. M. Paul and H. J. Siegert (Eds.), An Conf. on very Large Data Bases, ACM, Sept. Advanced Course on Distributed Systems -- Architecture any Imp~ementat[on, Springer-Verlag, N~-York, MY, 1980. "This work concentrates on the problem of incompatible data models "Accessing multiple, heterogeneous, transformation, the criteria of remote Database Management Systems correctness of such transformations, promises to be difficult because of and methods of construction of correct differences in: i) the data model transformations being defined". [See employed, ill data structures also (Ka]inichenko, 1q76)]. constructed using this data model, iii) Database Management System functionality differences, iv) L. A. ~a]inichenko, "Relational-Network differences in Data Manipulation Data gtructure Mapping", G. M. Nijssen Languages used in interacting with the (Ed.} , Modelling in Data Base Management data structures, and v) computer system Systems-'-T~'--IIFT'P--~C2 ~ing Conf. on differences. Imposing a uniform user Modelling in Data Base Management Syst., viewpoint across this collection of Jan. 197~), North-Holland, Amsterdam, differences is an alternative to Neth., Ig~6, pp. ~3-~09. requiring detailed user knowledge of the characteristics of each of the "Mapping is considered" [between] accessed systems". [See also "n-ary relations" [and] "network data". (Kimbleton, Wang, and Fong, 1979)]. [~ee also (~alinichenko, 197~)].

S. R. Kimbleton, P. S.-C. Wang, and E. N. M. H. ~ay, "An Assessment of the CODASYL Fong, "XNDM= An Experimental Network Data DDL for Use With a Relational Subschema", Manager", Proc. 4th Berkeley Conf. on B. C. M. Douqu6 and G. M. Nijssen (Eds.) , Distributed Data Management and Computer Data Base Description (Proc. IFIP TC-2 Networks, NTIS, Aug. 1979, pp. 3-17. p~ i aT---Wo rl~q---i~ n6~['? on Data Base Description, Jan. ]g~5), North-Holland, "This paper describes" [a] "research Amsterdam, Neth., 1975, pp. 199-214. project concerned with establishing the feasibility, issues, alternatives, and "This paper investigates the a technical approach for supporting a possibi]ity of accessing a DDLC network data manager". "The basic database described by a DDLC schema assumption underlying the design ... is through a subschema presenting the user heterogeneity of data models, data with a relational view of the structures, DBMSs, DMLs and computer database". "The argument will proceed systems on which these DBMSs reside". by first describing some of the ways [The paper describes] "superimposing a relations might be based on network uniform user viewpoint". [See also structures yielding consistent effects (Kimbleton and Wang, 1980)]. on retrieval, and by then considering for each of these 'derivation rules' the effect of updating a relation". A. C. Klug, "Theory of Database Mappings", Ph.D. thesis, Dept. of Computer Sci., U. of Toronto, Toronto, Ont., Canada, Dec. L. ~erschberg, A. C. ~lug, and D. C. 197g; Computer Syst. Research Group Tech. Tsichritzis, "A Taxonomy of Data Models", Rep. 98. P. C. Lockemann and E. J. Neuhold (Eds.% , Systems for Large Data Bases (Proc. 2nd "Definitions of structure and operation "T'nt~f'~'-'Y~on~. on Very Large Data Bases, mappings are given". [Mappings can be SePt. 1976), North-Holland, Amsterdam, between schemas, between schema and Neth., 1q77, pp. 43-~4. subschema, between data models, between levels (e.g., logical and physical), or "This paper classifies a collection of between multiple-node and single-node conceptual data models within a queries in a distributed data base]. taxonomy framework consisting of the fo]]owing parameters: graph theoretic versus set theoretic models, A. C. Klug and D. C. Tsichritzis, mathematical foundations, terminology, "Multiple View Support Within the and semantic levels of abstraction". ANSI/SPARC Framework", Proc. 3rd Intl. Conf. on Very Large Data'-~'~s,--A~M,-'~c ."

"Features for the conceptual mode] are discussed". [This is based upon the language described in (Tsichritzis,

- 62 - 1975%]. "Three external models part of the compiler". [The latter corresponding to the hierarchical, language can use tuple-at-a-time network and relational approach are access, as does the CODASYL DML. See mapped onto the conceptual model" also (Astrahan et al., Ig76)]. [See also (gchmid and Bernstein, 1975) and (Tsichritzis, 1975)]. J. R. Lucking, "Comments on Advantages of the Data Structure Set Model", in (Rustin, J. A. Larson, H. R. Johnson, and J. D. 1974), pp. 115-119. Lawrence, "Multimodel Data Base Management", Sperry Univac Research Rep. "At the declarative level of describing TMASS731, Rosevi]le, MN, Oct. 197R. data, there is virtually no difference between networks and relations. At the "An intermediate data model is manipulative level, the comparisons described which acts as a stepping that we have seen today have been stone to bridge the differences between slightly unfair, in that one is CODASYL and relational data models. compar ins systems of a sl ightly Information preserving transformations different level of procedurality. The are described which may be mechanically constraints imposed upon DBTG in applied to data definition or data defining language are the constraints manipulation statements of one data imposed by COBOL". mode] to obtain equivalent statements in the other data model. Using these transformations it is possible to W. C. McGee, "A Contribution to the Study design a multimode] DBMS which supports of Data Equivalence", J. W. Klimbie and K. both network and relational data L. Moffeman (Eds.) , Data Base Management mode] s". [See a] so (Johnson and (Proc. IFIP TC-2 Working Conf. on Data Larson, 1979~ , (Johnson, Larson, and Base Management, Apr. 1974), Lawrence, 1979), and (Johnson, Larson, North-Holland, Amsterdam, Neth., 1974, pp. and Lawrence, I~)]. 12~-148.

"The paper presents a set of techniques R. M. Lee, "Comparison of HI-TQ and the for transforming structures of one Relational Calculus", Dept. of Decision particular" "data structure class (or Sciences working paper 7R-~7-~5, the DSC)" "into equivalent structures of a Wharton School, U. of Pennsylvania, second DSC. As the first DSC, we will Philadelphia, PA, July 1978. take the Flat Data Structure Class". "As the second DSC, we will take the "Paper compares the retrieval class implicit in the data description capabilities of HI-IQ, a non-procedural language of the CODASYL Data query language for Network type Description Language Committee". databases, to the Relational Calculus".

W. C. McGee, "On User Criteria for Data R. M. Lee, "A Short Survey of Current Data Model Evaluation", ACM Trans. on Database Models", Dept. of Decision Sciences Syst., vol. I, no.----~,--EfEZ -T97E, pp. working paper 7R-S2-~7, the Wharton TTE:7s7. School, U. of Pennsylvania, Philadelphia, PA, Feb. lqTR. "An evaluation procedure is needed which will allow the user to evaluate "This paper presents a brief tutorial alternative models in the context of a on several of the more popular 'data specific set of applications". "Two models' or logical representations used kinds of criteria are presented: use in database systems to characterize the criteria, which measure the usability structural aspects of the database". oF the mode]; and implementation criteria, which measure the implementability of the mode] and the R. A. Lorie and J. F. Nilsson, "An Access efficiency of the resulting Npecif~cation Languaqe for a Relational implementation. The use of the Data Base System", IBM J. Research and criteria is illustrated by applying Development, vol. 23~'--~o.-n[, ~y~'3-g~T~, E. them to three specific models: an 2~5-29R. n-ary relational model, a hierarchic model, and a network model". "We address the problem of executing high level language queries submitted to a relational data base system. As a L. I. Mercz, "Issues in Building a step in the process of constructing an Relational Interface on a CODA~YL DAMS", 'efficient' compiler for a high level G. Bracchi and G. M. Nijssen (Eds.) , Data language we suggest the elaboration of Base Architecture (Proc. IFIP TC-2 Wor]EEEg an intermediate level language acting Conf. on Data Base Architecture, June as a target language for the optimizer 197Q), North-Holland, Amsterdam, Neth.,

- 63 1979, pp. 191-~II. record types (which may be a set of files from a file system or record "The CODASYL'Ve database proposals are types / segments in a DBMS) into a evaluated and found to be insufficient number of relations". For providinq a semantically complete, Formal description for the conceptual schema. Therefore, it is not possible E. J. Neuhold, "Data Mapping: Formal to derive a complete relational view Hierarchical and Relational Model", R. from a CODASYL schema. In contrast Rustin (Ed.) , Data Base Systems (Courant with the CODASYL'7R proposals, a Computer Sc[. Symp. 6, May 1971), procedural external schema and related Prentice-Hall, Englewood Cliffs, NJ, 1972, data manipulation operators are p. 185 (abstract); "Data Mapping: A outlined, which can coexist with Formal Hierarchica] and Relational View", normalized relational views on the same Institute For Appl. Informatics, U. of information base". Karlsruhe, Karlsruhe, W. Germany, Feb. 1973.

A. ~. Michaels, B. Mittman, and C. R. "The techniques developed for the Carlson, "A Comparison of the Relational formal description of the semantic of and CNDASYL Approaches to Data-Base programming languages can be applied to Management", Computing Surveys, ACM, vol. the different data constructs found in ~, no. I, Mar. ]97~, pp.--~'~-~-CT~l. data base systems". "This paper concentrates on hierarchical "Data definition, manipulation, organisations ..., and compares some of protection, and independence, and their properties to the relational view system performance are important of data". factors when studying and evaluating data-base management systems". "The relational and CODAeYL Data Base Task G. M. Nijssen, "Data Structuring in the Group approaches ... are compared and DDL and Relational Model", J. W. Klimbie contrasted from these points of view. and K. L. ~offeman (Eds.) , Data Base The paper concludes with the Mana gemen ~ (Proc. IFIP TC-2 Working Conf. observation that since data-base on Data Base Management, Apr. 1974), manaqement systems are to serve the North-Holland, Amsterdam, Neth., 1974, pp. needs of widely diverse communities of 363-384. users, no single approach to data-base management seems either desirable or "The main data structuring elements of likely to emerge as dominant in the the CODASYL DDL and Relational Data near Future". Model are compared. The comparison is illustrated with an example and some data descriptions. The main conclusion E. Nahouraii, L. O. Brooks, and A. F. is that a common DDL could be Cardenas, "An Approach to Data specified, encompassing the main Communication Between Different aspects of the CODASYL DDL and Generalized Data Base Management ~ystems", Relational Data Model. An instant P. C. Lockemann and E. J. Neuhold (Eds.) , guideline for DDL users" [for Systems For Larqe Data Bases (Proc. ~nd relational-like use] "and some DDL Intl. ConT. on ~ry Larqe Data Bases, modifications are also shortly qeDt. 1q~6) , North-Holland, Amsterdam, described". Neth., lg~7, pp. 117-I~.

"mbis report discusses some of the T. W. Olle, The CODASYL Approach to Data problems and provides a methodology For Base Management, Jo n~W~y and Sons, New communicating and exchanging ~r~'~]~, NY, I-~T~[, Chap. 24 ("Relational information between heterogeneous Approach"), pp. 266-279. models of data or DBMSS that are commercially available". "Our proposed [This chapter defines various aspects approach to interconnecting of the relational data model and heteroqeneous DBM~s is to characterize compares them with aspects of the the access paths into and through the CODASYL data model. See also (Olle, data in a DIAM string catalog". [See 1975)]. also (Cardenas and Pirahesh, 19~@)].

T. W. Of]e, "Current and Future Trends in S. R. Navathe, "An Intuitive Approach to Data Base Management Systems", Proc. IFIP Normalize Network Structured Data", Proc. Congress 74, North-Holland, A~T~Fr a~, 6th Intl. Conf. on very Large Data Bases, Net-~., Aug. 1974, pp. 99R-1006.

[Tn part of this paper], "the work of [This paper describes] "a simple the CODASYL Data Base Task Group and of procedure For converting a network of the groups which it has spawned is

- 64 - compared with that of the Guide-Share o~ data models". [See also (Hardgrave groups and with the emerging theories and Sibley, 1979)]. on relational data bases. The significant features of Codd's work are selected and their potential impact J. B. Ruby and A. G. Carrick, "An Approach assessed". to Providing a Re]ationa] Query Processor for a Limited CODASYL Data Base Management System", Proc. 3rd USA - Japan Computer • . W. O1]e, "Data Definition Spectrum and Conf., AFIPS, Oct. T97~--pp.-~i1212[~ Procedurality Spectrum in Data Base Management Systems", J. W. Klimbie and K. "A dual Data Base Management System L. Roffeman (Eds.) , Data Base Management (DBMS) design is proposed within which (Proc. IFTP TC-2 Work'S-- L~n6]~.--on Data both network and relational subsystems Base Management, Apr. 1974), coexist. The network subsystem serves North-Holland, Amsterdam, Neth., 1974, pp. as the 'operational' DBMS with which 28g-293. programmers interface, while it also provides the base upon which the "This paper describes two spectrums - relational end user (query only) the phys-log spectrum along which all subsystem operates". "The basic data definition languages must lie and network subsystem ... is a limited the procedurality spectrum along which subset of the 1976 CODASYL a]] languages to act on a computerized specifications; and the proposed data base must lie. A proposal for a relational query interface is a limited multi-stage data definition process subset of ... SEQUEL". supported by different user interfaces is outlined". [See also (Olle, Ig~4cI]. R. Rustin {Ed.1 , Proc. ACM S[GMOD [STGFIDET] Workshop on Data ~6"script~, Access, and Control, voW.- 2 f"Data Models: T. W. O]le, "Data Structuring Facilities Data-Structure-Set versus Relational") , in Commercially Available DBMS", Computer May 1974. Bulletin, British Computer Soc., series 2, no. I, Sept. 1g~4, pP. 2~-22 and 3~. "This, the second volume, contains the papers and the transcript of the debate "This paper introduces the new concept on the differences and similarities of of a complete spectrum of data the Data-Structure-Set Model versus the definition facilities from the purely Relational Model of data between C. W. logical to the completely physical. An Bachman and E. F. Codd". [This indication is given of where major includes six papers ((Bachman, 1974), commercially available DBMS lie in this (Codd and Date, 1978), (Date and Codd, spectrum. The interaction with this ]974), (Lucking, 1974), (Sibley, 1974), spectrum of processing languages on and (Tsichritzis, 1974)) plus various procedural ]evels is discussed. discussion]. Finally, a potentia] future role For the relational database and its associated processing language is H.A. Schmid and P. A. Bernstein, "A suggested" [gee also (Olle, 19~4b)]. Multi-level Architecture for Relational Data Base Systems", Proc. [1st] Int]. Conf. on Very Large Data Bases, ACM, Sept. T. W. O]]e, "A Practitioner's view of ]975, pp. 202-22~. Relational Data Base Theory", FDT, ACM SIGMOD, vo]. 7, no. 3-4, ]g75, pP~"~-~. "We describe a multi-level architecture for relational data base systems". "The ... paper represents a lightly [One level supports the language edited version of" [fOlle, 19781]. described in (Tsichritzis, 1976). See also (Mlug and Tsichritzis, 1977) and (Tsichritzis, 1975)]. 7. g. Rothnie and W. T. Hardgrave, "Data Mode] Theory: A Beginning", Proc. Fifth Texas Conf. on Computing £yst.-[----lq~E~'L2C~7 L. S. Schneider, "A Relational Query T~.-- T~, --~. 47 (abstracT; Tech. Rep. Compiler for Distributed Heterogeneous 1@, Dept. of Info. Syst. Management, U. of Databases", Sterling Systems Corp., Maryland, College Park, MD, Sept. ]976. Golden, CO; presented at SHARE 50 Conf., Mar. 1978. "We propose that 'data model' be used to denote: a collection of abstract "Information systems in which the entities, facilities for defining database is distributed among many abstract entities", [and] "a co]lection heterogeneous representations are of operations that manipulate abstract becoming more common with the advent of entities". "This paper represents an computing networks". "This paper embrionic attempt to establish a theory contends that a mapping from a

- 65 - consistent comprehensive user-view to E. H. Sibley, "On the Equivalences of Data the semantics o~ each target system Based Systems", in (Rustin, 1974), pp. involved would reduce this problem to 43-76. one o{ syntax £or which known solutions may be applicable, and that such a "The two major approaches that have mapping can be founded on the emerged may be termed the relational or relational model the Data set theoretic, and the data structured ~ndependent Accessing Model ..., and or procedural. There are obviously the juxtaposition o{ these". [See also differences in these, but there are (Schneider, Iq75%]. also similarities".

L. S. ~chneider, "A Relational View of the E.H. Sibley and L. Kerschberg, "Data Data Independent Accessing Model", Proc. Architecture and Data Model ACM-gIGMOD Intl. Conf. on Management o~ Considerations", Proc. Natl. Computer T~-~a, June ~, pD~. 5-~. Conf., AFIPS, vo~'--216, June 1977, pp. 85-96. "This paper attempts to show that the DIAM's relevance to contemporary "In the past, attempts have been made research in database systems can be to compare and contrast ... systems, enhanced by viewing it through n-ary but the greatest difficulty arises in relations. To accomplish this, the seeking a common basis. This paper paper first develops a redefinition of attempts to show how a generalized data the DIAM String Level in terms of n-ary system (GDS), represented by two relations. It then appeals to the different models, could form such a remaining levels of the DIAM to basis; it then proposes that data describe various relational policy definitions can restrict the GDS implementation alternatives". ~See to a specialized model, such as a also (Schneider, Iq78%]. relational or DBTG-like model".

D. W. Shipman, "The Functional Data Model M. R. Stonebraker and G. D. Held, and the Data Language DAPLEX", Proc. "Networks, Hierarchies, and Relations in ACM-SIGMOD IQTg Intl. Conf. on Management Data Base Management Systems", Proc. ACM Data, May ]~-9-d~ p. 59 (~stract~ ; to Pacific 75 Regional Conf. (Data: Its Use, appear ~n ACM Trans. on Database Syst.. Organ[Za~'on, and Management), Boole and Babbage, Inc., Sunnyvale, CA, Apr. 1975, "This paper presents and motivates the pp. l-g. DAPLEX language and the unaerlying data mode]" [One section states that] "the "The three models of data that data modelling capabilities of DAPLEX currently prevail are described. One incorporate those of the hierarchical, is the relational view". "The second relational and network models". is the network view advanced by CODASYL". "A third view is a hierarchical one". "Non-procedural B. ~hneiderman and G. N. Thomas, "Path languages for all three views of data Expressions for Complex Queries and are very similar". "The expressiveness Automatic Database Program Conversion", of the data structures is the same for" Proc. 6th Int]. Conf. on Very Large Data [relational and network]. ~-ases, ACM, r~ct. l~', pp. ~q-z14.

"our efforts to develop an automatic M. R. Stonebraker and L. A. Rowe, database system conversion facility "Observations on Data Manipulation yielded a powerfu], yet simple query Languages and their Embedding in General language which was designed for ease of Purpose Programming Languages", Proc. 3rd conversion". "This approach provides Intl. Conf. on Very Large Data Bases, ACM, for a high level, relational-like Oct. 19w7, Pp. 128-143. facility with the visual and structural appeal of the network mode]" "Within "Many data base query languages, both a set instance the records are in ... stand-alone and coupled to a general order by the set keys" [as in a CODASYL purpose programming language, have been set] "and duplicate set keys are not proposed" "Issues include the allowed" [as in a relation, whose specification of performance options, tuples are unique, or a CODASYL set side effects, implicitness, the with duplicates not allowed]. handling of types and the time of binding". "The emphasis is on a comparative analysis".

- 66 - K. Tabata, H. Matsumoto, and Y. Ohno, "A D. C. ~sichritzis, "A Network Framework DBMS for a Composite Type of Distributed for Relation Implementation", B. C.M. Data Base", Proc. 3rd UqA - Japan Computer Douqu~ and G. M. Nijssen (Eds.), Data Base Conf., ~FTPS, Nct. IQ~e, pp. Ig~-191. Description (Proc. IFIP TC-2 Spec~l Working Conf. on Data Base Description, "We propose a philosophy of a Data Base Jan. lq75), ~orth-Holland, Amsterdam, Management System (DBMS~ for a Neth., ]975, pp. 269-282. composite type of distributed data base. Component data bases being to "A network mode] is defined in terms of construct the distributed data base ... simple relationships among data". "A may have data models different from one network language is proposed to declare another. We integrate various kinds of and manipulate access paths between data models into the relational model data. It is claimed that the proposed to construct the distributed data framework can be appropriate as a basis base". for relation implementation". [See also (~lug and Tsichritzis, 1977), (Schmid and Bernstein, 1975), and N. Tha]mann and D. Thalmann, "A (Tsichritzis, 1976)]. Problem-Oriented Ana]ys~s of Database Models", J. Chemical Information and Computer S~Tences, American Chemical Sock, J. D. Ullman, Principles of Database Washington, PC, vo]. ]9, no. ~, May ]979, Systems, Computer ScienCe Press, PP. ~5-8q. Rockville, MD, 198~, Sect. 3.4 ("Comparison of the Models"), pp. 98-100. "Which is the most convenient considering specific "By the criterion of easy use, there is applications? The goal of this paper no doubt that the relational model is is to try to answer this question by superior". "When we consider the the use of a chemical example. potential for efficient implementation, Examples of requests describe the the network and hierarchical models problems of insertion, deletion, and score high marks". updating; these requests are analyzed for the hierarchical model and are expressed in a relational language Y. Vassiliou and F. H. Lochovsky, "DBMS defined by the authors and in Socrate Transaction Translation", Proc. COMPSAC for the network model" 90, IEEE-CS, Oct. 19R~, pp. ~9-9~; an ~tended version, by Y. Vassiliou, appears in F. H. Lochovsky (Ed.) , "A Panache of D. C. Tsichritzis, "Comments on Advantages DBMS Ideas If", Computer Syst. Research o6 the Relational view", ~n (Rustin, Group Tech. Rep. 10], U. of Toronto, 1974~, pp. 77-81. Toronto, Ont., Canada, May 1979, pp. 92-122. "The principal advantages of the relational model are: simplicity, in "Data translation and transaction terms of the data and the language; translation are two major problems that uniformity, everything is based on one have to be solved in order to achieve concept; completeness, it is as the coexistence of heterogeneous complete as anything else; data distributed databases". "Methods for independence, both in storage structure mapping a hierarchical or network and growth independence for certain schema to an equivalent relational kinds of changes in the schema; schema are presented" "Relational security and integrity". operators _ . are translated to equivalent "hierarchical and network operations". D. C. Tsichritzis, "LSL: A Link and ~elector Language", Proc. ACM-SIGMOD Intl. Conf. on Management of Data, June 1976, R. E. Westgaard, "A COBOL Data Base pp. I~-133. Facility for the Relational Data Model", Proc. ACM Pacific 75 Regional Conf. (Data: "This paper presents the main ideas ~---U~, ~--d~a~za~]on, a~ ~[anagement) , behind the language LgL". "It can be Boole and Babbage, Inc., Sunnyvale, CA, thought of as a relational system Apr. 1975, pp. Iq2-139. implemented on a network environment". [gee also (Klug and Tsichritzis, 1977), "The relationa] data model ... has been (Schmid and Bernstein, 1975), and contrasted with the CODASYL DDL network (Tsichritzis, ]g~5)]. model as to effectiveness in meeting the goals of data independence, flex~bi]ity in data modeling, and ease of use". "The CODASYL DDL and DML interfaces are oriented to the application programmer whereas the

- 67 - re3at~ona] model is oriented to the "An algorithm is presented for less procedural non-programmer. This designing relational views over network paper proposes an application schemas". "The particular declarations programmer COBOL interface for the of a CODASYL schema which supply relational model utilizing existing sources of logical data definition are COBOL !/O verbs and the CODASYL DDL first identified. Then the view design constructs of schema and subscbema". algorithm is derived on the basis of a formal analysis of the semantic constraints established by these v. K. M. Whitney, "Relational Data declarations. A new form of data Management Tmplementation Techniques", structure diagram is also introduced to Proc. ACM S!~MOD [~IGFIDET] Workshop on visualize these constraints". [See Descrlp~, Access, and Control, Ma-~ also (Goldman, 1979), (Zaniolo, 1979b) , "~'~F, pp. 321'-~4~.-- and (Zaniolo, 1977)].

[In part of this paper], "the concepts o~ modeling informat{on structures with C. A. Zaniolo, "Multimodel External data ~s illustrated w~th the CODA~YL Schemas for CODA~YL Data Base Management Dm~G and the relational models". Systems", G. Bracchi and G. M. Nijssen (Eds.) , Data Base Architecture (Proc. IFIP TC-2 Wor~ng Conf. On Data Base E. Wong and R. H. Katz, "Logical Design Architecture, June 1979), North-Holland, and Schema Conversion for Relational and Amsterdam, Neth., 1979, pp. 171-190. DRTG Databases", P. P.-S. Chen (Ed.) , Proc. Intl. Con6. on Entity-Relationship "The problem of designing and ~ac~ to Systems Analys~s and Design, supporting relational and hierarchical Dec. l~TD-~ pp. 9~g'L-~;-----~ate{ pub~d views over CODASYL network schemas is as Entity-Re]ati0nsh~ p Approach to ~ystems considered". "A solution is proposed Analysis and Design, NortH-Holland, based on the integrity constraints on Amsterdam, Ne~., logical data resulting from certain declarations in the CODASYL Data "A variant oF the Entity-Relationship Definition Language". [See also mode] is proposed as the data model for (Goldman, 197g), (Zaniolo, 1979a) , and logical design". "Mapping rules will (Zaniolo, 1977)]. be proposed for transforming a design schema ~nto a corresponding schema of either relational or DB~G type". "It C. A. Zaniolo, "Relational Views in a Data is shown that with relatively minor Base System: Support for Queries", Proc. semantic augmentation of DBTG and COMPSAC 77, IEEE-CS, Nov. 1977, pp. relational ~ata models, the mapping ~s 267-~5. reversible. As a consequence, reversible schema conversion between "The relational mode] is extended to DBTG and re]ationa~ models becomes include null values and operations on possib3e". relations containing null values. These concepts allow the definition of information preserving relational views C. Wood, R. C. gummers, and E. B. over a network schema. A mechanism is wernandez, "Authorization in Multilevel presented to support queries on these Database Models", Information Syst., views without duplication of actual Pergamon Press, nxford, UK, vol. 4, no. ~, data". [See also (Goldman, ]979), 1979, pD. 155-I~1. (Zanio]o, 1979a), and (Zaniolo, 1979b) 3. "In a mult{leve] database architecture, authorization rules may be written at the conceptual level or at the external K. Zimmermann, "Different Views of a Data level. We analyze here the consistency Base: Coexistence Between Network Model o~ author{zation rules written at these and Relational Model,', Proc. list] Intl. two levels. We assume that the Conf. on Very Large Data Bases, ACM, Septl conceptual ]eve] model is of the -[-c~, pp.-~T~-~. entity-relationship type and the external model is relational" "The problem of data base access via different data models has been investigated for the network model and C. A. Zanio]o, "Design o~ Relational Views the relational model. The network Over Network Schemas", Proc. ACM-gIGMOD model is based on ... Codasyl .... For l q~g Intl. Conf. on Manage~en-~ ~ a given network model of the data base ~ ~.--1"7~-I ~---~-'~-~ht~-~ ]~nger a coexistent relational model is version is "Design o ~ ~e]ationml Views proposed. The proposal ~s based on an ~ver a Network Schema", ~perry Research extension of the usual relational model Center ReD. ~CRC-RR-nR-37, Sudbury, MA, ... by an incorporation of appropriate July ]97~ . network parameters".

-68~