On Semantics of Reactive Rule-Based Systems

In this paper we address special issues which arise when the rule-based programming paradigm is emlployed in development of reactive realtime systems. We begin by presenting a rule-based language which has emerged while developing intelligent cruise control systems. We describe a naive operational semantics based on an an implemented inference engine, and explain why the semantics is not appropriate in safety-critical real-time contexts. We then define a number of correctness criteria ensuring termination, consistency and determinism, based on a formal declarative semantics. However, the declarative semantics is non-constructive. In order to be able to build an implementation satisfying the correctness criteria, two alternative approaches are proposed. Both approaches build upon static checks of a rule-based program. In the first approach some correctness criteria are met by accepting only stratified programs after the static checks. In the second approach we accept programs which are ..