Towards local search for answer sets

Abstract

Answer set programming has emerged as a new important paradigm for declarative problem solving. It relies on algorithms that compute the stable models of a logic program, a problem that is, in the worst-case, intractable. Although, local search procedures have been successfully applied to a variety of hard computational problems, the idea of employing such procedures in answer set programming has received very limited attention. This paper presents several local search algorithms for computing the stable models of a normal logic program. They are all based on the notion of a conflict set, but use it in different ways, resulting in different computational behaviors. The algorithms are inspired from related work in solving propositional satisfiability problems, suitably adapted to the stable model semantics. The paper also discusses how the heuristic equivalence method, that has been proposed in the context of propositional satisfiability, can be used in systematic search procedures that compute the stable models of logic programs. © Springer-Verlag Berlin Heidelberg 2002.