On the Expressiveness of Distributed Leasing in Linda-like Coordination Languages

Distributed leasing is an emerging paradigm adopted in applications based on the client-server architecture. The basic idea is that, at the moment a client asks for a service, it also declares the (maximal) duration that service should be granted. This paradigm has been recently adopted by SUN Microsystems in the definition of JavaSpaces, a coordination middleware inspired by the shared dataspace model of Linda. In this paper we investigate the interplay between distributed leasing and the Linda coordination model. To this aim, the output operation of a Linda-like calculus is adapted to enrich the tuple with expiration time; the semantics of the resulting calculus is studied under both assumptions that there is one unique global clock or many local clocks. We prove that the introduction of distributed leasing strictly decreases the expressiveness of the Linda-like calculus, and that global time is stricly more expressive than local time. 1. Work partially supported by Esprit working group n.24512 “Coordina”