Communication as unification in process algebras: Operational semantics

Abstract

Process algebras are formal systems aimed at the abstract description of computing devices organized as collections of components which can operate in parallel and cooperate by communicating values among them. In classical process algebras, communication is by rendez-vous, where symmetric proposals made by two processes meet synchronously: a local variable proposed by a receiving process is bound to a value proposed by a sending process. In this paper, this binary rendez-vous with only one variable on one side and one value on the other side is viewed as a mere special case of a more general situation for communication by synchronous rendez-vous. An arbitrary number of processes may offer terms to each others: if these terms have common instances, communication can indeed take place, and amounts to applying the unifying substitutions to the processes involved. The syntax and operational semantics of process algebras with this general view of communication are formally defined. The operational semantics show how this generalization leads to a clean formalization of the notion of global variables in process algebras. Applications are presented, which show that these algebras implement an original computing paradigm, where computation is achieved solely by means of communication.