Truth versus information in logic programming

Abstract

The semantics of logic programs was originally described in terms of two-valued logic. Soon, however, it was realised that three-valued logic had some natural advantages, as it provides distinct values not only for truth and falsehood but also for undefined. The three-valued semantics proposed by Fitting (Fitting, M. 1985. A Kripke-Kleene semantics for logic programs. Journal of Logic Programming 2, 4, 295-312) and Kunen (Kunen, K. 1987. Negation in logic programming. Journal of Logic Programming 4, 4, 289-308) are closely related to what is computed by a logic program, the third truth value being associated with non-termination. A different three-valued semantics, proposed by Naish, shared ..