TEMPORAL LOGICS IN AI - SEMANTICAL AND ONTOLOGICAL CONSIDERATIONS

One way to represent temporal information in a logical formalism is by associating 'proposition types' with time points or time intervals. The way this is usually done in AI is by 'reifying' propositions, so that what otherwise would have been formulas actually appears as arguments to some 'predicate,' say TRUE, as in TRUE(t//1, t//2, COLOR(HOUSE, RED)). This way time is referred to explicitly, while retaining its special notational and conceptual status. We examine this method by looking closely at two of the more influential formalisms featuring reified propositions. We show that these do not have completely clear semantics, and that they make some unfortunate and unnecessary ontological commitments. Finally, we present a new formalism and demonstrate that it does not suffer from these disadvantages.