-calculus, Internal Mobility, and Agent-passing Calculi -calculus, Internal Mobility, and Agent-passing Calculi

The-calculus is a process algebra which originates from CCS and permits a natural modelling of mobility (i.e., dynamic reconngurations of the process linkage) using communication of names. Previous research has shown that the-calculus has much greater expres-siveness than CCS, but also a much more complex mathematical theory. The primary goal of this work is to understand the reasons of this gap. Another goal is to compare the expres-siveness of name-passing calculi, i.e., calculi like-calculus where mobility is achieved via exchange of names, and that of agent-passing calculi, i.e., calculi where mobility is achieved via exchange of agents. We separate the mobility mechanisms of the-calculus into two, respectively called internal mobility and external mobility. The study of the subcalculus which only uses internal mobility, called I, suggests that internal mobility is responsible for much of the expres-siveness of the-calculus, whereas external mobility is responsible for much of the semantic complications. A pleasant property of I is the full symmetry between input and output constructs. Internal mobility is strongly related to agent-passing mobility. By imposing bounds on the order of the types of I and of the Higher-Order-calculus San92] we deene a hierarchy of name-passing calculi based on internal mobility and one of agent-passing calculi. We show that there is an exact correspondence, in terms of expressiveness, between the two hierarchies. Extracts of parts of the material contained in this paper can be found in the Proceedings of TAPSOFT'95 and ICALP'95.-calculus, mobilit e interne et calculs agent-passing R esum e : Le-calculus est une alg ebre de processus dont l'origine remonte a CCS et qui permet d'obtenir un mod ele naturel de mobilit e (c-ad , des reconngurations dynamiques de la structure de communication des processus) en utilisant la communication par noms. Des recherches pr ec edentes ont montr e que le-calculus a une expressivit e plus grande que CCS, mais aussi une th eorie math ematique plus complexe. L'un des objectifs de ce travail est de comprendre les raisons de cette dii erence. Un autre objectif est de comparer l'expressivit e de calculs name-passing, c-ad de calculs comme le-calculus o u la mobilit e est obtenue par l' echange de noms, et celle de calculs agent-passing, c-ad de calculs o u la mobilit e est obtenue par l' echange d'agents. Nous s eparons les m ecanismes de mobilit e du-calculus en deux, et parlons de mobilit e interne et de mobilit …