Efficient Fixpoint Computation in Linear Tabling

摘要

Early resolution mechanisms proposed for tabling such as OLDT rely on suspension and resumption of subgoals to compute fixpoints. Recently, a new resolution framework called linear tabling has emerged as an alternative tabling method. The idea of linear tabling is to use iterative computation rather than suspension to compute fixpoints. Although linear tabling is simple, easy to implement, and superior in space efficiency, the current implementations are several times slower than XSB, the state-of-the-art implementation of OLDT, due to re-evaluation of looping subgoals. In this paper, we present a new linear tabling method and propose several optimization techniques for fast computation of fixpoints. The optimization techniques significantly improve the performance by avoiding redundant evaluation of subgoals, re-application of clauses, and reproduction of answers in iterative computation. Our implementation of the method in B-Prolog not only consumes an order of magnitude less stack space than XSB for some programs but also compares favorably well with XSB in speed.