COMPUTER-AIDED SOFTWARE DEVELOPMENT Daniel Teichroew, Ernest Allen Hershey III, and Yuzo Yamamoto ISDOS Project, University of Michigan, Ann Arbor, Michigan, USA. Beizer, Holzman, and Kent (1975). Abstract 1.1.1 Classification of Systems. The terms such as systems, information systems, information In recent years, as the hardware cost/capability processing systems are used with widely different ratio has continued to decrease and as much of the meanings. The meanings in which they are used in routine data processing has been computerized, the this paper are defined in this section and emphasis in software development has shifted from illustrated in the example in Figure 1.1.1. just getting systems operational to the maintenance of existing systems, reduction of Organization duplication by integration, selective addition of new applications, systems that are more usable, An organization is a legal entity, or sub-unit of maintainable, portable and reliable and to a legal entity, that is uniquely and specifically improving the productivity of software developers. identifiable. Usually an Information System is a part of an organization which has a basic function This paper examines a number of trends that are other than information processing. In Figure changing the methods by which software is being 1.1.1 the example of an organization is a produced and used. More and more of the research Manufacturing Enterprise. and development is now being directed towards producing systems that have the desirable Organizational SHb-systemS properties mentioned above. Also, more computer-aided tools are being developed and made An organization may have a number of sub-systems available. The most important trend probably is which are used to accomplish, or contribute to the the introduction of software development support accomplishment, of the basic function. One of facilities which provide an integrated set of these subsystems is an Information System. In tools, based on a central computerized data base. Figure 1.1.1, the Manufacturing Enterprise has At this stage, these systems perform primarily sub-systems such as Production, Logistics, clerical work but gradually their facilities are Distribution, Finance, etc. being expanded. A number of research and development efforts are concerned with moving Information Systems closer to the ultimate objective of producing executable software for a particular computing The Information System is the sub-system of an environment directly from a set of functional organization in which information (in the form of requirements. data) is received, recorded, processed, stored, retrieved and transmitted. The Information System A large part of the software developed today is may consist of an informal system and (formal) still custom built to meet a specific set of Information Processing Systems. The informal requirements in a specific computing environment. system consists of all the information processing Considerable effort is being directed towards in which data is not recorded. reducing the amount of software that must be newly produced each time by making use of software that Information Processing Systems already exists. The subsystems of the Information System in which Many of the concepts and techniques in which these data are recorded and processed following a formal developments are based are not new. Many tools procedure are called Information Processing are available but are not widely used. The Systems. Two kinds of Information Processing availability of technology does not necessarily Systems may be distinquished: manual and mean that it will be used. Some of the reasons computer-based. Manual systems are those in which for this are examined as a basis for the all operations are performed manually. consideration of issues involved in practical Computer-based information processing systems are application of new system development technology. those in which some operations (though not necessarily all) are performed by a computer. 1. Software Environment Since this paper is primarily concerned with computer-based systems, the term Information 1.1 Computer Based Information Processing Systems Processing System will be used to refer to alia. Related Terminology Computer-based Information Processing Systems. Each Information Processing System consists of Large amounts of resources are being devoted to some non-computerized procedures, a data base, development and maintenance of computer based application software, and a computing system as information processing systems, i.e., systems that indicated in Figure 1.1.1. include hardware, software and other components. Much of the concern with the efficiency and 1.1.2 Classification of Software. Software effectiveness of these systems today is focused on may be subdivided into components at various the software e.g., "software is the problem". levels: System, subsystem, module, and statement. This paper is primarily concerned with software development, however it is desirable to first Software System. A software system is a place software in its proper context within collection of software components that, if used systems. Terminology is not yet standard in this together, accomplish a complete information field, and it is therefore necessary to start with processing function. a number of definitions. In general these are consistent with those used in the recent Software Subsystem. A software subsystem is a encyclopedias by Ralston and Meek (1976) and part of software system that, if used together, - 189 - accomplishes a separately defined part of the product. This differs from the simple whole software system's function. In very complex program in all of the above ways. It costs software systems it may be useful to distinguish nine times as much. But it is the truly more than one level of software subsystems. useful object, the intended product of most system programming efforts." Software Components. Software components are parts of software system that constitute basic Software is frequently classified as either system individual units such as programs, routines, software or application software. System Software1 subroutines, modules, units of data description is used during the execution of other software; and executable modules. it includes operating systems, monitors, etc. It is necessary because the application software Software Module. The smallest part of a software cannot run on the raw hardware itself. system that can be utilized by a software Application Software includes software components component at the same or higher level to tailored to the user's needs, including all accomplish a defined function. software products that are not part of system software as defined above. Statement. The smallest self-contained component of a Software System which can be expressed in the The application area that is of most concern in source programming language. this paper is that of software development. All programs supporting the development of software, In a particular system, these definitions can be such as assemblers, compilers, translators, made more specific since they depend on the program generators, design-aid packages and the operating system under which the system is to be like are included in this classification. run and the programming language in which it is written. Since the discussion in this paper is It will be convenient to distinguish between independent of operating systems and programming generalized software and custom-tailored software. languages, the terms system, subsystem module, and Generalized Software is software produced to meet statement will be used with the general meaning the needs of a number of users for the same given above. general application in different organizations and different computing environments. Custom-tailored Software may be classified by its operational Software is software designed to meet specific status. An excellent taxonomy is given by Brooks requirements in a specific situation and for a (1975) Figure 1.1.1: specific environment. 1.2 Environment in Which Software la Developed and "In the upper left of Fig. 1.1.2 is a Used program. It is complete in itself, ready to be run by the author on the system on Since software is developed in many different which it was developed... circumstances and used in many different situations, it is desirable to classify the There are two ways a program can be different cases and to attempt to identify some converted into a more useful, but more parameters which characterize them. Boehm (1976) costly, object. These two ways are p. 1239, considers the application of software represented by the boundaries in the engineering to two areas: diagram. AREA 1 : Detailed design and coding of system Moving down across the horizontal boundary, software by experts in a relatively a program becomes a programming product. economics-independent context. This is a program that can be run, tested, repaired, and extended by anybody. It is AREA 2: Requirements analysis, design, test and usable in many operating environments, for maintenance of applications software by many sets of data... technicians in an economics-driven context. Promotion of a program to a programming The parameters that he considers in distinguishing product requires its thorough between Areas 1 and 2 are: documentation, so that anyone may use it, fix it, and extend it. As a rule of thumb, - whether the requirements analysis is done before I estimate that a programming product costs or after the at least