A Generalized QSQR Evaluation Method for Horn Knowledge Bases

Abstract

We generalize the QSQR evaluation method to give the first set-oriented depth-first evaluation method for Horn knowledge bases. The resulting procedure closely simulates SLD-resolution (to take advantages of the goal-directed approach) and highly exploits set-at-a-time tabling. Our generalized QSQR evaluation procedure is sound and complete. It does not use adornments and annotations. To deal with function symbols, our procedure uses iterative deepening search which iteratively increases term-depth bound for atoms and substitutions occurring in the computation. When the term-depth bound is fixed, our evaluation procedure runs in polynomial time in the size of extensional relations.

On the efficiency of query-subquery nets

“…Researchers have developed a number of evaluation methods for Datalog deductive databases such as the top-down methods QSQ [14,1], QSQR [14,8,9], QoSaQ [15] and the bottom-up method Magic-Set [1,2,3,12] (which combines the magic-set transformation with the improved semi-naive evaluation method). As mentioned earlier, some of these methods have been generalized for Horn knowledge bases [8,11,7].…”

“…As mentioned earlier, some of these methods have been generalized for Horn knowledge bases [8,11,7].…”

“…It is set-oriented and uses a tabulation technique. As discussed in [8], that version is incomplete. In [8], Madalińska-Bugaj and Nguyen corrected and generalized the QSQR method to give a set-oriented depth-first search evaluation method for Horn knowledge bases.…”

“…Horn knowledge bases are thus a generalization of Datalog deductive databases. Both the QSQR and Magic-Set evaluation methods of Datalog have been generalized for Horn knowledge bases [8,11,7].…”

On the Web Ontology Rule Language OWL 2 RL

“…The Horn fragment of predicate logic without function symbols also has PTime data complexity. Furthermore, as shown in [25], evaluation methods of Datalog can be extended to Horn knowledge bases in predicate logic without function symbols. Therefore, we propose the following extensions of OWL 2 RL 0 :…”