Experience Using EMYCIN James s. Bennett and Robert S. Engelmore

The development of expert systems is plagued with a well-known and crucial bottleneck: in order for these systems to perform at all the domainspecific knowledge must be engineered into a form that can be embedded in the program. To this end the purpose and structure of two quite dissimilar rule-based systems are reviewed. Both systems were constructed using the EMYCIN system after interviewing an expert. The first, SACON (Bennett et al., 1978), meant to assist an engineer in selecting a method to perform a structural analysis; the second, CLOT (Bennett and Goldman, 1980), is meant assist a physician in determining the presence of a blood clotting disorder. The presentation of the details of these two systems is meant to accomplish two functions. The first is to provide an indication of the scope and content of these rule-based systems. The reader need not have any knowledge of the specific application domain; the chapter will present the major steps and types of inferences drawn by these consultants. This conceptual framework, what we term the inference structure, forms the basis for the expert's organization of the domain expertise and, hence, the basis for successful acquisition of the knowledge base and its continued maintenance. The second purpose of this chapter is to indicate the general form and function of these inference structures.