Indeterminate concurrent constraint programming: a fixpoint semantics for non-terminating computations
Sven-Olof Nyström, Bengt Jönsson · 1993
This paper presents a semantics for non-deterministic concurrent constraint programming languages. The semantics address the issues of giving an adequate treatment of non-terminating computations, in particular with fairness and liveness, and giving a compositional semantics, where the meaning of a recursively defined program is obtained as a fixpoint. We present a simple concurrent constraint programming language with a reduction rule semantics, which is augmented with fairness requirements. We specify how traces are obtained from fair computations of a program. The operational semantics of a program is defined as the set of traces of the program. We show that this trace semantics can be defined compositionally. The trace semantics is transformed into a continuous fixpoint semantics, using the framework of Lehmann's category-theoretic constructions, and present a general schema for defining continuous operators on the semantic domain. A simple abstraction operator is defined, and is p...