Internal mobility and agent-passing calculi

Abstract

In process calculi, mobility indicates the possibility of dynamic reconfigurations of the process linkage. Name- passing calculi like the π-calculus achieve mobility via communication of names. The names exchanged can be internal or external. Accordingly, we can distinguish between internal and external mobility. In [San94b] it is shown that the subcalculus of the π-calculus which only uses internal mobility, called πI, has a simple algebraic theory but, at the same time, is expressive enough to encode, for instance, the λ-calculus. In this paper, we compare name-passing calculi based on internal mobility with agent-passing calculi, i.e., calculi where mobility is achieved via exchange of agents. By imposing bounds on the order of the types of πI and of the Higher-Order π-calculus we define 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. This refines and complements previous results on the comparison between name-passing and agent-passing calculi by Thomsen, Sangiorgi and Amadio.