XSB: A system for efficiently computing well-founded semantics

Abstract

The well-founded model provides a natural and robust semantics for logic programs with negative literals in rule bodies. We implemented the well-founded semantics in the SLG-WAM of XSB [19]. Performance results indicate that the overhead of delay and simplification to Prolog-or tabled-evaluations is minimal. To compute the well-founded semantics, the SLG-WAM adds to an efficient tabling engine for definite programs three operations-negative loop detection, delay and simplification-which serve to detect, to break and to resolve cycles through negation that might arise in evaluating normal programs. XSB is a full Prolog system that closely approximates the ISO standard; additionally, it supports a tight integration of tabled predicates with nontabled predicates.