Abstract

There are many calculi for reasoning about concurrent communicating processes which have locations and are mobile. Examples include the original Ambient Calculus and its many variants, the Seal Calculus, the MR-calculus, the M-calculus, etc. It is desirable to use such calculi to describe the behavior of mobile agents. It seems reasonable that mobile agents should be able to follow non-predetermined paths and to carry non-predetermined types of data from location to location, collecting and delivering this data using communication primitives. Previous type systems for ambient calculi make this di#cult or impossible to express, because these systems (if they handle communication at all) have always globally mapped each ambient name to a type governing the type of values that can be communicated locally or with adjacent locations, and this type can not depend on where the ambient has traveled. We present a new type system PolyA where there are no global assignments of types to ambient names. Instead, the type of an ambient process P not only indicates what can be locally communicated but also gives an upper bound on the possible ambient nesting shapes of any process P # to which P can evolve, as well as the possible capabilities and names that can be exhibited or communicated at each location. Because these shapes can depend on which capabilities and names are actually communicated, the types support this with explicit dependencies on communication. PolyA is thus the first type system for an ambient calculus which provides type polymorphism of the kind that is usually present in polymorphic type systems for the #-calculus. 1

Citations