Synchronous Calculus of Communicating Systems

Abstract

Asynchronous algebras such as CCS can help us to understand and correctly design concurrent systems by viewing them as collections of concurrently operating sequential subsystems; the behaviour of each subsystem is defined in terms of sequences of atomic actions, internal ones to progress a subsystem’s local task and external ones for subsystem interaction. By formalising such a view, the calculus predicts the behaviour of a composition from knowledge of the behaviours of its individual parts. But, being an asynchronous algebra, it is constrained to express system behaviours in terms of sequences of actions, independent of time, and cannot directly address real-time systems. On the other hand, synchronous algebras (which, by definition, contain a concept of global time - events only happen when some omnipresent clock ticks) define not only the order of actions but also when they occur.