On the Termination of Logic Programs with Function Symbols

Recently there has been an increasing interest in the bottom-up evaluation of the semantics of logic programs with complex terms. The main problem due to the presence of functional symbols in the head of rules is that the corresponding ground program could be infinite and that finiteness of models and termination of the evaluation procedure is not guaranteed. This paper introduces, by deeply analyzing program structure, new decidable criteria, called safety and Γ-acyclicity, for checking termination of logic programs with function symbols under bottom-up evaluation. These criteria guarantee that stable models are finite and computable, as it is possible to generate a finitely ground program equivalent to the source program. We compare new criteria with other decidable criteria known in the literature and show that the Γ-acyclicity criterion is the most general one. We also discuss its application in answering bound queries.