A poorly designed knowledge base can be as cryptic as an arbitrary program and just as difficult to maintain. Representing inference procedures abstractly, separately from domain facts and relations, makes the design more transparent and explainable. The combination of abstract procedures and relational language for organizing domain knowledge provides a generic framework for constructing knowledge bases for related problems in other domains, and also provides a useful starting point for studying the nature of strategies. In HERACLES, inference procedures are represented as abstract metarules, expressed in the form of the predicate calculus, organized and controlled as rule sets. A compiler converts the rules into LISP code and allows domain relations to be encoded as arbitrary data structures for efficiency. Examples are given of the explanation and teaching capabilities afforded by this representation. Different perspectives for understanding HERACLE's inference procedure and how it defines a relational knowledge base are discussed in some detail. (Fifteen figures and 67 references are provided.) (Author)