Patterns of interaction in rule-based expert system programming

We study the effect of adding a rule to a rule-based heuristic classification expert system, in particular, a rule that causes an unforeseen interaction with rules already in the rule set. We show that it is possible for such an interaction to occur between sets of rules, even when no interaction is present between any pair of rules contained in these sets. A method is presented that identifies interactions between sets of rules, and an analysis is given which relates these interactions to rule-based programming practices which help to maintain die integrity of the knowledge base. We argue mat the method is practical, given some reasonable assumptions on the knowledge base.