Extensions to Rules for Explanation and Tutoring

As described in Part Eight, the success of MYCIN as a problem solver suggested that the program’s knowledge base might be a suitable source of subject material for teaching students. This use of MYCIN was consistent with the design goals that the program’s explanations be educational to naive users and that the representation be flexible enough to allow for use of the rules outside of the consultative setting. In theory, the rules acquired from human experts would be understandable and useful to students. The GUIDON program discussed in Chapter 26 was developed to push these assumptions by using the rules in a tutorial interaction with medical students. In attempting to "transfer back" the experts’ knowledge to students through GUIDON, we found that the experts’ diagnostic approach and understanding of" rules were not explicitly represented. GUIDON cannot justify the rules because MYCIN does not have an encoding of how the concepts in a rule fit together. GUIDON cannot fully articulate MYCIN’s problem-solving approach because the structure of the search space and the strategy for traversing it are implicit in the ordering of rule concepts. Thus the seemingly straightforward task of converting a knowledge-based system into a computer-aided instruction program has led to a detailed reexamination of the rule base and the foundations on which rules are constructed, an epistemological study. In building MYCIN, rule authors did not recognize a need to record the structured way in which they were fitting rule parts together. The rules are more than simple associations between data and hypotheses. Sometimes clause order counts for everything, and different orders can mean differ-