A Frame-Based Production System Architecture

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 . . ..-........... *This research was supported in part by ONR contract N0001479C-0302 and by .NIH Biotechnology Resource Grant RR-00785. 54 slots are those worth investigating cornfirmed or denied respectively assertions are suggesfivilies). Implicit in the production rule if the original assertion is (numbers following these representation is a fimction which indicates how to compute the “belief’ of the consequent assertions given belief in the antecedent assertion. Unfortunately, evaluation of the antecedent assertion involves modal logic (since greater shading is required than simple binary values for belief and disbelief). Therefore, a “HowToDetermineBelief’ slot is associated with each assertion indicating how its belief is to be computed. If: 1) The severity of Obstructive Airways Disease of the patient is less than or greater to mild, al’;1 2) The number of pack-years smoked is greater than 0, and 3) The number of years ago that the patient quit smoking is 0 Then: It is definite (1000) that the following is one of the conclusion statements about this interpretation: Discontinuation of smoking should help re1iev.e the symptoms. OADwithSmoking: Manifestation