Concurrency and Concurrent Constraint Programming

The intent of this paper is to provide the basic ideas and the possible alternatives underlying the task of giving a semantics to a concurrent system/language, and to describe a particular approach which makes some speciic choices in order to give a semantics to the class of CC languages. In particular, we will discuss how to handle the issues of concurrency and nondeterminism, and we will examine in detail the formalism of Petri nets, which, suitably extended, we will then use for CC languages. In our semantics for CC programs, the meaning of a program is in fact a net where the concurrency present in all computations, as well as the nondeterminism, can be naturally seen. We will also point out several extension of the basic semantics, that can be used for more complex classes of CC languages, like those with atomic tells, or with two kinds of nondeterminism.