The Structure of the MYCIN System

A number of constraints influenced the design of the MYCIN system. In order to be useful, the system had to be easy to use and had to provide consistently reliable advice. It needed to be able to accommodate the large body of task-specific knowledge required for high performance, a knowledge base that is subject to change over time. The system also had to be able to use inexact or incomplete information. This applies not only to the absence of definitive laboratory data, but also to the medical domain itself (which is characterized by much judgmental knowledge). Finally, to be useful interactive system, MYCIN needed to be capable of supplying explanations for its decisions and responding to physicians’ questions, rather than simply printing orders. The MYCIN system comprises three major subprograms, as depicted in Figure 4-1. The Consultation Program is the core of the system; it interacts with the physician to obtain information about the patient, generating diagnoses and therapy recommendations. The Explanation Program provides explanations and justifications for the program’s actions. The Knowledge-Acquisition Program is used by experts to update the system’s knowledge base.