What Are Polymorphically-Typed Ambients?

Abstract: The Ambient Calculus was developed by Cardelli and Gordon as a formal framework to study issues of mobility and migrant code. We consider an Ambient Calculus where ambients transport and exchange programs rather that just inert data. We propose different senses in which such a calculus can be said to be polymorphically typed, and design accordingly a polymorphic type system for it. Our type system assigns types to embedded programs and what we call behaviors to processes; a denotational semantics of behaviors is then proposed, here called trace semantics, underlying much of the remaining analysis. We state and prove a Subject Reduction property for our polymorphically typed calculus. Based on techniques borrowed from finite automata theory, type-checking of fully type-annotated processes is shown to be decidable; the time complexity of our decision procedure is exponential (this is a worst-case in theory, arguably not encountered in practice). Our polymorphically-typed calculus is a conservative extension of the typed Ambient Calculus originally proposed by Cardelli and Gordon

Typed Mobile Objects

. We describe a general model for embedding object-oriented constructs into calculi of mobile agents. The model results from extending agents with methods and primitives for message passing. We then study an instance of the model based on Cardelli and Gordon's Mobile Ambients. We define a type system for the resulting calculus, give a subject reduction theorem, and discuss the role of the type system for static detection of run-time type errors and for more program verification purposes. 1 Introduction Calculi of mobile agents are receiving increasing interest in the programming language community as advances in computer communications and hardware enhance the development of large-scale distributed programming. Independently of the new trends in communication technology, object-oriented programming has established itself as the de-facto standard for a principled design of complex software systems. Drawing on our earlier preliminary work on the subject [2], in this paper we dev..