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.