Contextual occurrence nets and concurrent constraint programming

Abstract

This paper proposes a new semantics for concurrent constraint programs. The meaning of each program is defined as a contextual net, which is just a usual net where context conditions, besides pre- and post-conditions, are allowed. Context conditions are just items which have to be present in order for an event to take place, but which are not affected by the event. They are very useful for describing situations where different events share a common resource and want to read it simultaneously. In fact, such events are concurrent in the net. The causal dependency relation of the net induces a partial order among objects in the same computation, while its mutual exclusion relation provides a way of expressing nondeterministic information. Such information can be of great help to a scheduler while trying to find an efficient execution of the program, or also to a compile-time optimizer.

Research partially supported by the GRAGRA Basic Research Esprit Working Group n.7183, the ACCLAIM Basic Research Esprit Working Group n.7195 and Alenia S.p.A.