A Domain-Independent System that Aids in Constructing Knowledge-Based Consultation Programs

摘要

This thesis demonstrates an effective domain-independent system, called EMYCIN, for constructing one class of expert computer programs: rule-based consultants. Such a consultant uses knowledge specific to a problem domain to provide consultative advice to a client. Domain knowledge is represented in EMYCIN primarily as production rules, which are applied by a goal-directed backward-chaining control structure. Rules and consultation data may have associated measures of certainty, and incomplete data are allowed. The system includes an explanation facility that can display the line of reasoning followed by the consultation program, or answer questions from the client about the contents of its knowledge base. Other built-in human-engineering features allow the system architect to produce, with a minimum of effort, a consultation program that is pleasing in appearance to the client. To aid the system designer in producing a knowledge base for a domain quickly and accurately, EMYCIN provides a terse, stylized, but easily understood language for writing rules; performs extensive checks to catch common user errors, such as misspellings; and handles all necessary bookkeeping chores. To improve efficiency in a running consultation program, EMYCIN provides a rule compiler that transforms the system's production rules into a decision tree, eliminating the redundant computation inherent in a rule interpreter. It then compiles the resulting tree into machine code. The program can thereby use an efficient deductive mechanism for running the actual consultation, while the flexible rule format remains available for acquisition, explanation, and debugging.