A production system for speech understanding

Abstract

A production system was developed for syntactic and semantic processing within the Hearsay-II speech understanding system. The major properties of the system are discussed, including (1) conversion of static language descriptions into productions, (2) compilation and data-directed execution of productions, (3) dynamically modifiable thresholds on goodness of pattern matches, (4) partial matching, and (5) representation and integration of bottom-up, top-down and horizontal searches. Several weaknesses of the production system paradigm in this application appeared during the course of this research. These arose from (1) the arbitrariness of canonical decompositions of patterns into subpatterns, (2) insufficient use of contextually confirming evidence for individual hypotheses due to the narrowness (literality) of monitored conditions, and (3) difficulty in evaluating the varying import of the same generic action in different contexts. Thus, while the uniformity and lack of explicit organization of production systems are touted as their most desirable features, attendant difficulties of dynamically organizing and controlling coherent problem solutions must be seriously considered in problem domains requiring careful allocation of computational resources.