Efficient Instance Retrieval of Subgoals for Subsumptive Tabled Evaluation of Logic Programs

TL;DR

This paper introduces an efficient algorithm and data structure extension for instance retrieval of subgoals in subsumptive tabling, significantly improving performance in logic program evaluation.

Contribution

It presents a novel algorithm and data structure extension for efficient subgoal instance retrieval in subsumptive tabling, enhancing performance and scalability.

Findings

Performs well on complex benchmarks

Handles large numbers of subgoals without degradation

Improves answer sharing in logic programming

Abstract

Tabled evaluation is an implementation technique that solves some problems of traditional Prolog systems in dealing with recursion and redundant computations. Most tabling engines determine if a tabled subgoal will produce or consume answers by using variant checks. A more refined method, named call subsumption, considers that a subgoal A will consume from a subgoal B if A is subsumed by (an instance of) B, thus allowing greater answer reuse. We recently developed an extension, called Retroactive Call Subsumption, that improves upon call subsumption by supporting bidirectional sharing of answers between subsumed/subsuming subgoals. In this paper, we present both an algorithm and an extension to the table space data structures to efficiently implement instance retrieval of subgoals for subsumptive tabled evaluation of logic programs. Experiments results using the YapTab tabling system show that our implementation performs quite well on some complex benchmarks and is robust enough to handle a large number of subgoals without performance degradation.