Application Design: Issues in Expert System Architecture

We describe an expert system that has been applied to the task of application design. Users supply the system with problem specifications, such as the required output data, and the system produces a graphic representation of the completed application in the form of a flow diagram. The application design task has forced us to consider two important issues in expert system architecture: constraint processing and the explicit representation of control flow. The resulting knowledge representation and control logic are discussed. I Introduction Computers are commonly used in a wide variety of application design areas. Building the application programs, however, is often a difficult and frustrating task requiring the blending of both domain-specific and computer-specific expertise. It is frequently the case that the application problem expert is not a computer expert and must seek the help of appropriate computer professionals whose availability and skills may be limited. This problem has received considerable attention and work is proceeding along several paths in pursuit of an effective solution [1,2 ]. This paper presents an expert system which assists in preparing a well-formed definition of a desired application. This definition is presented in the form of a program flow chart showing the proper configuration of input devices, data processing functions, and output devices needed to produce the desired result. The flow chart is developed from a knowledge base which includes representations of data transformations valid within the problem domain. For example, if the problem domain is payroll applications a transformation relating GR0SS_PAY to NET_PAY would be represented in the knowledge base and would include references to data processing functions required to enact the transformation. A notable feature of application definition is the dual nature of the expertise required; an effective consultant must have knowledge of both the specific application domain (e.g., payroll applications) and of more general application design principles. Several interesting problems in expert system architecture have been encountered, especially in the areas of constraint processing and control flow. A discussion of these areas comprises the bulk of this paper. We begin, however, with an elaboration of the task performed and a discussion of our choice of knowledge representation and constraint architecture. I The Task Figure 1 shows a flow diagram of a simple payroll application. The task of the system is to produce this chart from an initial statement of the desired program outputs. The system is expected to select appropriate devices …