Real-time software life cycle with the model system

摘要

The main theme of the paper concerns use of an assertive specification language for real-time software development and maintenance. It is used for asserting the facts or relations inherent in the problem to be solved, as opposed to conventional programming languages, which are used to express the computer solution. Expressing a problem in Model consists of declaring array variables and defining their relationships through equations. This is radically different from conventional programming, which relates the problem in terms of computer operations. The language is supported by an automatic system which interacts with the user in soliciting missing definitions or correcting inconsistencies, and which translates the specification into a near-optimal computer solution. The main advantages of this approach are in: 1) the direct role assumed by nonprogrammer problem-domain analysts in the real-time system development and maintenance, 2) savings in development time, 3) obtaining more reliable programs, and 4) reusing existing components and interconnecting existing and new components in maintenance of the system. The Model methodology consists of use of three automatic components: 1) a configurator that produces command language programs for globally synthesizing program units — called modules — and for setting up their communications, 2) a compiler that produces individual module programs from detailed specifications, and 3) a timer that evaluates worst case module processing delays. The Model system operates on Digital's VAX computers under the VMS operating system and on IBM's computers under VM and MVS operating systems. The software development is carried out using a host computer, and the programs are transferred to the target computing network. The paper starts with an overview of use of Model in real-time software development and maintenance. The differences from conventional programming are stressed through an example, which also illustrates th- use of the three above-listed automatic components of the Model system.