The Constraint Logic Programming (CLP) Scheme merges logic programming with constraint solving over predefined domains. In this paper, we study proof methods for universal left termination of constraint logic programs. We provide a sound and complete characterization of left termination for ideal CLP languages which generalizes acceptability of logic programs. The characterization is then refined to the notion of partial acceptability, which is well-suited for automatic modular inference. We describe a theoretical framework for automation of the approach, which is implemented. For non-ideal CLP languages and without any assumption on their incomplete constraint solvers, even the most basic sound termination criterion from logic programming does not lift. We focus on a specific system, namely CLP(R), by proposing some additional conditions that make (partial) acceptability sound

This paper describes a method for proving termination of queries to logic programs based on abstract interpretation. The method uses query-mapping pairs to abstract the relation between calls in the LD-tree associated with the program and query. Any well founded partial order for terms can be used to prove the termination. The ideas of the query-mapping pairs approach have been implemented in SICStus Prolog in a system called TermiLog, which is available on the web. Given a program and query pattern the system either answers that the query terminates or that there may be non-termination. The advantages of the method are its conceptual simplicity and the fact that it does not impose any restrictions on the programs.

Abstract. A logic program strongly quasi-terminates when only a finite number of distinct atoms (modulo variable renaming) are derivable from any given query and computation rule. This notion of quasi-termination, though stronger than related notions that only consider Prolog’s computation rule, is essential for ensuring the termination of partial evaluation, where liberal selection policies are often mandatory to achieve a good specialization. In this paper, we introduce sufficient conditions for the strong termination and quasi-termination of logic programs which are based on the construction of size-change graphs. The class of strongly quasi-terminating logic programs, however, is too restricted. Therefore, we also introduce an annotation procedure that annotates those predicate arguments which are responsible of the non-quasi-termination. As a consequence, the annotated program behaves like a quasi-terminating program if annotated arguments are generalized (i.e., replaced by a fresh variable) when they occur in a computation. We illustrate the usefulness of our approach by designing a simple partial evaluator in which global termination is always ensured offline (i.e., statically). A prototype implementation demonstrates its viability. 1

We introduce the notion of bounded nondeterminism for logic programs and queries. A program and a query have bounded nondeterminism if there are finitely many refutations for them via any selection rule. We o#er a declarative characterization of the class of programs and queries that have bounded nondeterminism by defining bounded programs and queries. The characterization is provided in terms of Herbrand interpretations and level mappings, in the style of existing characterizations of universal termination.

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