Tree{Based Fixpoint Iteration for Disjunctive Logic Programs

Non{Horn programs containing disjunctive rules allow for more advanced applications of deductive databases. But the inference process dealing with rapidly increasing amounts of disjunctive facts becomes much more intricate, because of the problems of nding resolvable atoms in the facts and of subsumption elimination in sets of facts. We present an eecient implementation of the xpoint computation for the disjunctive consequence operator T S P based on the {iteration technique and on a compact data structure of so{called clause trees for disjunctive facts. These trees speed up the combinatorial search in a T S P {hyperresolution step. Furthermore, the necessary operations of subsumption elimination can be performed eeciently based on them. The presented techniques can be used for computing the extended generalized closed world assumption of a disjunctive logic program and the generalized disjunctive well{founded semantics of a disjunctive normal logic program as well.