Efficient Retrieval of Subsumed Subgoals in Tabled Logic Programs

Tabling based systems use call similarity to decide when a tabled subgoal should produce or consume answers. Most tabling engines do that by using variant checks. A more refined method, named call subsumption, considers that a subgoal A will consume answers from a subgoal B if A is subsumed by B, thus allowing greater answer reuse. Recently, we have 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 an algorithm to efficiently retrieve the set of currently evaluating subgoals that are subsumed by a more general subgoal.