Discarding Unused Temporal Information in a Production System

Reasoning about temporal facts and continuous operation are two features needed by industrial expert systems. The interplay of those two requirements calls for some form of knowledge management for temporal information in order to limit memory consumption and to avoid performance degradation. The paper presents a method to remove obsolete temporal facts in the context of PAMELA-C, a rule-based production system language. Temporal conditions may be specified in the form of time intervals of fixed length between discrete events containing numerical time-stamps. The proposed algorithm discards partial matches as soon as the temporal constraints of the corresponding rule can no longer be satisfied. The run-time system then automatically removes events which cannot contribute to the reasoning process any longer. Keywords: knowledge maintenance, production systems, temporal information, RETE algorithm. 1 Introduction Many industrial expert system applications require some form of temporal ..