Donald Bren School of Information and Computer Sciences

Time is fundamental in representing and reasoning about changing domains. A proper temporal representation requires characterizing two notions: (1) time itself, and (2) temporal incidence, i.e. the domain-independent properties for the truth-value of fluents and events through-out time. Formally defining them involves some problematic issues such as (i) the expression of instantaneous events and instantaneous holding of fluents, (ii) the dividing instant problem and (iii) the formalization of the properties for non-instantaneous holding of fluents.

This paper discusses how previous attempts fail to address all these issues and presents a simple theory of time and temporal incidence which satisfactorily overcomes all of them.

Our theory of time, called IP, is based on having instants and periods at equal level. Our theory of temporal incidence is defined upon IP. Its key insight is the distinction between continuous and discrete fluents.