Can Actors and -Agents Live Together??

The syntax and semantics of actors and-agents is rst de-ned separately, using a uniform, \unbiased" approach. New coordination primitives are the added to the union of the two calculi which allow actors and-agents to cooperate. The syntax and semantics of actors and-agents are rst deened separately, using a uniform, \unbiased" approach. Since we aim at modeling concurrent distributed systems, and thus we are interested in asynchronous behavior, we choose for comparison with actors an asynchronous version of the-calculus. In the paper, the behavior of both actors and-agents is deened by certain logic sequents called tiles. A tile is a rewrite rule which describes a possible evolution of a part s of the system which is matched by it. In addition, a tile also describes the evolution of the interfaces of s with the rest of the system. Thus two parts s and s 0 sharing an interface can be rewritten only by tiles which agree on the evolution of the common interface. This restriction introduces a powerful notion of synchronization 3 among tiles, and also makes possible to see the synchronization of two tiles as a (larger) tile. Eventually, all the possible evolutions are obtained by the repeated composition (synchronized, or in sequence, or in parallel) of certain small basic tiles called rewrite rules. In the case of actors and-agents, it is convenient to take a coordination 19] point of view and to distinguish between the behavior of agents in isolation and the behavior of coordinators, i.e. of system components whose role is to connect agents and to control their behavior. This approach allows us to abstract from the behavior in the small of agents, which is presented in a state transition, syntax-independent form, and to focus on the behavior of coordinators, which are the most characteristic feature of distributed systems. Correspondingly, we distinguish between two kinds of rewrite rules: activity rules and coordination rules. An activity rule describes an evolution of a single sequential agent, and may ? 3 Even in an asynchronous system, synchronization is required to model the reception of messages and the extrusion of names.