A Data ow Semantics for Constraint Logic Programs

This paper introduces an alternative operational model for constraint logic programs First a transition system is introduced which is used to de ne a trace semantics T Next an equivalent xpoint se mantics F is de ned a data ow graph is assigned to a program and a consequence operator on tuples of sets of constraints is given whose least xpoint determines one set of constraints for each node of the data ow graph To prove that F and T are equivalent an intermediate semantics O is used which propagates a given set of constraints through the paths of the data ow graph Possible applications of F and O are discussed in particular its incrementality is used to de ne a parallel execution model for clp s based on asynchronous processors assigned to the nodes of the program graph Moreover O is used to formalize the Intermittent Assertion Method of Burstall Bur for constraint logic programs