Asynchronous Rendez-vous in Distributed Logic Programming

In this paper the semantics of the communication mechanism of the distributed logic programming language DLP is studied. DLP combines logic programming with object oriented features and parallelism. For an abstract subset of DLP both an operational and denotational semantics is given. The language DLP supports active objects, method call by rendezvous and moreover (distributed) backtracking over the results of such a rendezvous. To enable further exploitation of parallelism, the rendezvous provided is asynchronous. A distinction is made between the creation of a process for evaluating the method call on the one hand, and the request for an answer on the other hand. To model this communication mechanism (syntactic) resumptions are employed. The notion of a resumption explains the backtracking taking place in the asynchronous rendezvous. In addition, resumptions facilitate the systematic comparison of the operational and denotational semantics presented.