OLDTNF-based evaluation method for handling recursive queries in deductive databases

Abstract

OLDTNF resolution is an important mechanism used in a Prolog interpreter. This mechanism is extended and improved for evaluating recursive queries in deductive databases. The key idea of the refinement is to distinguish between two classes of lookup nodes in an OLDTNF derivation and to handle them differently. First, reduce the search space by cutting of any subtree rooted at a lookup node of the first class. Further, speed up the evaluation by processing the second class in a second phase and generate many solutions directly from the solutions already produced (and the corresponding keys of solution lists) instead of evaluating them by expanding the corresponding subtrees in terms of the new solutions stored in solution lists.