COMPUTING PRACTICES System Design for Usability Richard A. Demers IBM Information Systems Division 1. Introduction Computers are a major tool for SUMMARY: The factors underlying system design for usabil- increasing productivity. The accept- ity are examined and the role and responsibilities of a usability ability of computers to their users is, committee described. Under the control of a usability com- therefore, of growing importance. mittee, a balance between high levels of system function and Clerks and executives must be at- tracted to a computer system because usability was reached for the IBM System/38. The System/ of the enormous help it provides. 38 command language is presented to illustrate this balance. Martin [8] says, "To be effective, sys- tems will have to be designed from the outside in. The terminal or con- sole operator, instead of being a pe- cations and must be viewed as one of functions, however, can become a ripheral consideration, will become of the prime objectives of new com- barrier to usability unless equal at- the tail that wags the whole dog." puter systems. Ease of programming tention is paid to the quality and Ease of use is critical in making any is thus a prerequisite to increased consistency of their interfaces. tool attractive. usability on the part of clerks and Functions that eliminate con- It is primarily the application operators. cerns about the details of system op- programmer's responsibility to pro- Our paper examines the factors eration (by automating them) allow vide clerks and executives with usa- affecting system design for usability, users to concentrate on their appli- ble tools, but application program- especially for programmers. This is cation tasks. For example, System/ ming costs have escalated steadily done in terms of our experience in 38 storage management facilities au- over the last 20 years. As a result, it developing IBM System/38. tomatically manage both main mem- is increasingly difficult for a business ory and auxiliary storage as a single to both maintain its existing appli- 2. Functions and Interfaces address space and provide enhanced security and integrity [7, 10]. This is cations and develop new ones. In The Mythical Man-Month, a new function that alleviates many Growing programmer productivity Brooks [2] says, is, therefore, the key to usable appli- storage management and security The purpose of a programming system is to problems with which the application make a computer easy to use. To do this, it Permission to copy without fee all or part of furnishes languages and various facilities that programmer has had to cope. this material is granted provided that the 0ap- are in fact programs invoked and controlled Functions which provide unify- ies are not made or distributed for direct by language features. But these facilities are ing concepts also reduce the number commercial advantage, the ACM copyright bought at a price: The external description notice and the title of the publication and its of a programming system is 10 to 20 times of different interfaces that must be date appear, and notice is given that copying as large as the external description of the learned; e.g., the data management is by permission of the Association for Com- computer itself.... puting Machinery. To copy otherwise, or to facilities of System/38 provide a republish, requires a fee and/or specific per- Easy-to-use is not the same as sim- common interface to all types of fi!es mission. ple-to-use; it is also more than the supported by the system--i.e., data- Key words and phrases: usability, program- mer productivity, command language elimination of hard-to-use. At every base, diskette, tape, display, printers, CR Categories: 3.50, 4.35 step, the designer must actively or card files. This includes external Author's address: R.A. Demers, IBM Infor- search for functions and interfaces data description, program access, f'de mation Systems Division, Rochester, MN reference, and file override facilities 55901. which will enhance the effectiveness © 1981 ACM 0001-0782/81/0800-0494 75¢. of the programmer. A large number [6, 11]. This approach should be con- 494 Communications August 1981 of Volume 24 the ACM Number 8 trasted with add-on access methods which each have unique interfaces and peculiarities. Other examples of Work Station unifying concepts in the System/38 Operator / are object and library management s ~ functions [10l and a generalized mes- ,,/ sage handler [4]. / There still remain, however, a large number of functions and inter- faces for debugging and other pro- / Application / gramming tasks which must be / Programmer learned. Erhman [5] points out that I programmer productivity is bound Hardware by the programmer's need to know ! a large number of artificial, machine- oriented languages such as: --algorithmic "processing logic" t statement flow; roQ~a'~# t --external data description and con- ! ! version; CPF I i t --internal data typing and structur- f I % ing; % I % I --JCL or its equivalent; / System Service %% I --linkage editor or loader; / Operator Personnel I --absolute binary machine language / for reading dumps; --symbolic assembler language; Fig. 1. A Layered View of System/38 Functions and Interfaces. Each layer of function --debug and diagnostic system; provides interfaces for the next highest layer to use. Users are viewed as the outermost --utilities; layer. Different interfaces are provided for each user role. --text editor; --command procedures; --text formatter; --plain English. viewed as a significant barrier to us- tots, and service personnel) were in- Even this large set is not complete. ability. It is therefore obvious that cluded in the specifications .of Sys- Many of these functions produce special emphasis must be placed on tem/38 so designers could contin- output listings, displays, and mes- usability or the functional richness ually check their designs against the sages that the programmer must in- of a system will intimidate its users. needs of specific users. These de- terpret just to ascertain whether or scriptions included a listing of the not the requested function was per- 3. Subsets by User Role business responsibilities, of the tech- formed. If it was not, the program- Experiments by Carlise [3] on nical and administrative duties, and mer must know which procedures to Man Computer Interaction (MCI) of the qualifications and skills of the follow in order to correct the prob- demonstrated "that interface com- various types of users. Based on this, lem. It should come as no surprise plexity can be matched to user char- the system's functional capabilities then that a programmer's productiv- acteristics to improve MCI problem could be subset and its interfaces ity is dependent on an ability to learn solving effectiveness." It is impera- tailored to specific user roles. and retain this enormous mass of tive that system designers have a Figure I illustrates this subsetting data. thorough understanding of the var- of system interfaces. There is some The System/38 command lan- ious user roles--this in addition tO degree of overlap between user roles: guage illustrates the vast number of an appreciation of their functional Some users may cover more than one functions within today's systems. needs. A powerful but complex pro- user role (depending on the size and There are over 260 different Control gramming or command language complexity of the installation) and, Program Facilities (CPF) and utility which takes months to learn may be over time, a user may change roles. commands; user-defined commands appropriate for a professional pro- This subsetting by role cannot, there- can be created to extend this. The grammer, but it is not suitable for a fore, be rigid. Instead, it must be Command Language Reference data entry clerk or an executive. user-tailorable so as to meet the manual [12] is over 1,000 pages long. Descriptions of user roles (e.g., needs of the users' own organization. This large a command set can be clerks, programmers, system opera- Only the set of functions needed to 495 Communications August 1981 of Volume 24 the ACM Number 8 COMPUTING also blinds them to the interrelation- (CPF), the System/38 operating sys- ships between the components. Such tem. The committee had sufficient PRACTICES a problem becomes even more severe authority so that very few usability when major system functions, such issues needed to be brought to the as compilers and utilities, are devel- attention of management. It was do his/her job should be available to oped as separate products or in sep- possible for committee members to each user. If, over time, this set arate locations. Only when a signifi- work hand in hand with developers, changes to meet different business cant number of internal IBM loca- monitoring the development process needs, interfaces to the new function tions began to use System/38 did this on a daily basis, investigating and should be easy to learn. The consis- type of problem become obvious. Be- answering a myriad of little ques- tency of old and new interfaces fa- cause of the emphasis placed on tions, and refining usability stan- cilitates this learning process. other aspects of system usability, dards. CPF developers began to The System/38 command lan- however, correcting this problem did check with the usability committee guage is subset by user role through not require major redesign of either whenever a design change which command authorizations and by functions or interfaces. would affect a user interface was menus tailored to user roles. The contemplated. 5. The Usability Committee ability of the system to route a user The usability committee had re- to a particular application at sign-on Usability cannot be accom- sponsibility for: is also a means for controlling the plished by adding "ease-of-use" in- range of functions a user can per- terfaces.