Report Number: CS-TR-87-1168
Institution: Stanford University, Department of Computer Science
Title: Representing Control Knowledge as Abstract Task and Metarules
Author: Clancey, W. J.
Author: Bock, C.
Date: April 1985
Abstract: 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 a 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 a 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 HERACLES' inference procedure and how it defines knowledge bases are discussed in some detail.