Cuts and side-effects in and-or parallel Prolog

Abstract

Practical Prolog programs usually contain extra-logical features like cuts, side-effects, and database manipulating predicates. In order to exploit implicit parallelism from real applications while preserving sequential Prolog semantics, a parallel logic programming system should necessarily support these features. In this paper we show how Prolog's extra-logical features can be supported in an and-or parallel logic programming system. We show that to support extra-logical features an and-or parallel logic programming system should recompute the solutions to independent goals instead of sharing them. We describe an abstraction called the composition tree for representing and-or parallel execution with recomputation. We introduce the notion of “focal-leftmostness” in the composition tree and use it for deriving complete and efficient methods for supporting extra-logical predicates in and-or parallel logic programming systems based on the composition tree abstraction.