Preferred answer sets for ordered logic programs

Abstract

We extend answer set semantics to deal with inconsistent programs (containing classical negation), by finding a "best" answer set.Within the context of inconsistent programs, it is natural to have a partial order on rules, representing a preference for satisfying certain rules, possibly at the cost of violating less important ones.We showthat such a rule order induces a natural order on extended answer sets, the minimal elements of which we call preferred answer sets. We characterize the expressiveness of the resulting semantics and show that it can simulate negation as failure as well as disjunction.We illustrate an application of the approach by considering database repairs, where minimal repairs are shown to correspond to preferred answer sets. © 2002 Springer-Verlag.