In Non - Monotonic Extensions of Logic Programming

We present a framework of logic programming using an explicit representation of defeats of assumptions, called assumption denials. We study semantics for extended, disjunctive, and extended disjunctive programs, all in the same framework. The framework is based on a x-point operator over \uninterpreted programs", and semantics for various kinds of programs are then deened simply by adding appropriate constraint clauses. For extended programs, we present a skeptical semantics that is tractable, and a credulous semantics which is a natural extension of a number of equivalent semantics proposed for normal programs. The generality of this framework is further evidenced by its ability to deene semantics for disjunctive programs in terms of non-disjunctive programs. This reveals a relationship between disjunctive programs and non-disjunctive programs, which is known previously to be false in some other formalisms.