HEARSAY-III: A Domain-Independent Framework for Ex

Hearsay-Ill is a conceptually simple extenslon of the basic ideas in the Hearsay-II speech-understanding system [a]. That domaindependent expert system was, in turn, a product of a tradition of increasingly sophisticated production-rule-based expert systems. The use of production systems to encapsulate expert knowledge in manageable and relatively independent chunks has been a strong recurrent theme in Al. These systems have steadily grown more sophisticated in their pattern-match and action languages, and in their conflict-resolution mechanisms [la]. In this paper, we describe the Hearsay-Ill framework, concentrating on its departures from Hearsay-II. 1. The Heritage From Hearsay-II Hearsay-II provided two major advances -- the structuring of the workspace, called the bhckboard in Hearsay, and the structuring of the search, via scheduling mechanisms. The blackboard provided a two-dimensional structure for incrementally building hierarchical interpretations of the utterance: