A Descriptive Handling of Directly Conflicting Rules in Preferred Answer Sets

Abstract

We consider the problem of extending the answer set semantics for logic programs with preferences on rules. Many interesting semantics have been proposed. In this paper we develop a descriptive semantics that ignores preferences between non-conflicting rules. It is based on the Gelfond-Lifschitz reduction extended by the condition: a rule cannot be removed because of a less preferred conflicting rule. It turns out that the semantics continues to be in the hierarchy of the approaches by Delgrande et al., Wang et al., and Brewka and Eiter, and guarantees existence of a preferred answer set for the class of call-consistent head-consistent extended logic programs. The semantics can be also characterized by a transformation from logic programs with preferences to logic programs without preferences such that the preferred answer sets of an original program correspond to the answer sets of the transformed program. We have also developed a prototypical solver for preferred answer sets using the meta-interpretation technique.