Constructive Negation Under the Well-Founded Semantics

Constructive negation derives constraint answers for non-ground negative literals. Its incorporation into query evaluation under the well-founded semantics introduces two problems. One is the detection of repeated sub-goals and the elimination of redundant answers, which is required in order to guarantee termination. The other is the interaction between constraint answers of non-ground negative literals and recursion through negation. This paper presents SLG CN for eeective query evaluation with constructive negation under the well-founded semantics. It has two unique features. First, it supports reduction of constraint answers and redundant answer elimination and provides the rst termination result for goal-oriented query evaluation with constructive negation for function-free programs. Second, it avoids repeated computation in a subgoal. Even if a non-ground negative literal depends upon some ground negative literals whose truth values are not completely determined when they are selected, the constraints and bindings for variables in the non-ground negative literal can still be propagated once and for all.