A Frame-Based Production System Architecture

Abstract

We propose a flexible frame-structured representation and agenda-based control mechanism for the construction of production-type systems. Advantages of this architecture include uniformity, control freedom, and extensibility. We also describe an experimental system, named WHJXZE, that uses this formalism. The success of MYCIN-like production systems 141 [7] [9] has demonstrated that a variety of types of expertise can be successfully captured in rules. In some cases, however, rules alone are inadequate necessitating the USC of auxiliary representations (e.g. property lists for paramzters in MYCIN). Other limitations result from the use of goal-directed control. In this paper we outline a flexible schemata for constructing high performance production-like systems. The architecture consists of two components: 1. An extensible representation (utilizing a frame-structured language) which captures production rule knowledge. 2. An agenda-based control mechanism allowing considerable freedom in tailoring control flow. We have used this architecture in the development of a system named WHEEZE, which performs medical pulmonary function diagnosis based on clinical test results. This syst%m is based on two earlier efforts, PUFF [7], an EMYCIN-based production rule system Ill], and CENTAUR [l] 121, a system constructed of both rules and prototypes. AN ~LTERNATXVE RI~PRESENTATION FOH PRODUCTIONS Figure 1 shows how a typical PUFF rule would be transformed into our representation. Each assertion is represented as a frame in the knowledge. base, with anteccdcnt sub-assertions appearing in its h4auzjdarion slot. The number associated with each manifestation is its corresponding importance. Similarly, the certainty factor and findings from the rule are given separate slots in the assertion. Assertions appearing in the SuggesliveOf and ComplemenlaryTo