Reasoning about Continuous Change

The problem of formalising continuous change within reasoning about action systems such as the situation calculus has recently been receiving increasing attention ((Rei96], MS96]). In this paper we show that a long-existing systems theoretic reasoning methodology, that of Zeigler's DEVS (discrete event system speciication), not only subsumes the standard situation calculus but is able to elegantly describe continuous change within a discrete description structure. We demonstrate that on the semantic level both Reiter's recent formalisation of continuous change within the situation calculus, and Miller and Shana-han's formalisation of continuous change within the event calculus t neatly into a DEVS framework. Our results not only evince a signii-cant connection between logic-based action formalisms and the algebraic formalism of systems theory, and between reasoning about action and discrete event simulation, but also provides support for using DEVS|a well-studied and rigorously implemented framework|as an underlying semantic framework for reasoning about action formalisms.