Temporal Representation and Default Reasoning

Abstract

It is desirable for expert systems to deal with temporal knowledge. Expert systems such as ONCOCIN, MECS-AI are developed for this purpose, and one of the most populer mechanism was Allen's Interval Logic. In this paper, we propose a temporal knowledge representation and a reasoning mechanism on it which is based on Kowalski's Event Calculus. First, we define a primitive predicate which will enable us to represent many kinds of temporal knowledge uniformly, including the continuity of a state which Event Calculus can't deal with. And we define macro operators such as "since","till", "at" in order to represent the temporal knowledge easily. Next, for the consistency of the knowledge-base, we introduce an inconsistency check mechanism with the constraint about simultaneity. Then we propose a temporal reasoning mechanism with default about time which means "State will continue unless inconsistency occurs". In the process of the default reasoning, we also use the constraint about simultaneity. Finally, we present a simple example of the knowledge-base and the temporal reasoning on our system implemented in Prolog.