Non-termination Analysis Research Articles

A practical analysis of non-termination in large logic programs

AbstractA large body of work has been dedicated to termination analysis of logic programs but relatively little has been done to analyze non-termination. In our opinion, explaining non-termination is a much more important task because it can dramatically improve a user's ability to effectively debug large, complex logic programs without having to abide by punishing syntactic restrictions. Non-termination analysis examines program execution history when the program is suspected to not terminate and informs the programmer about the exact reasons for this behavior. In Liang and Kifer (2013), we studied the problem of non-termination in tabled logic engines with subgoal abstraction, such as XSB, and proposed a suite of algorithms for non-termination analysis, called Terminyzer. These algorithms analyze forest logging traces and output sequences of tabled subgoal calls that are the likely causes of non-terminating cycles. However, this feedback was hard to use in practice: the same subgoal could occur in multiple rule heads and in even more places in rule bodies, so Terminyzer left too much tedious, sometimes combinatorially large amount of work for the user to do manually.Here we propose a new suite of algorithms, Terminyzer+, which closes this usability gap. Terminyzer+ can detect not only sequences of subgoals that cause non-termination, but, importantly, the exact rules where they occur and the rule sequences that get fired in a cyclic manner, thus causing non-termination. This makes Terminyzer+ suitable as a back-end for user-friendly graphical interfaces on top of Terminyzer+, which can greatly simplify the debugging process. Terminyzer+ back-ends exist for the SILK system as well as for the open-source ${\cal F}$lora-2 system. A graphical interface has been developed for SILK and is currently underway for ${\cal F}$lora-2. We also report experimental studies, which confirm the effectiveness of Terminyzer+ on a host of large real-world knowledge bases. All tests used in this paper are available online.1In addition, we make a step towards automatic remediation of non-terminating programs by proposing an algorithm that heuristically fixes some causes of misbehavior. Furthermore, unlike Terminyzer, Terminyzer+ does not require the underlying logic engine to support subgoal abstraction, although it can make use of it.

Non-termination analysis of logic programs with integer arithmetics

AbstractIn the past years, analyzers have been introduced to detect classes of non-terminating queries for definite logic programs. Although these non-termination analyzers have shown to be rather precise, their applicability on real-life Prolog programs is limited because most Prolog programs use non-logical features. As a first step towards the analysis of Prolog programs, this paper presents a non-termination condition for Logic Programs containing integer arithmetics. The analyzer is based on our non-termination analyzer presented at International Logic Programming Conference (ICLP) 2009. The analysis starts from a class of queries and infers a subclass of non-terminating ones. In first phase, we ignore the outcome (success or failure) of the arithmetic operations, assuming success of all arithmetic calls. In second phase, we characterize successful arithmetic calls as a constraint problem, the solution of which determines the non-terminating queries.

Experiments with Non-Termination Analysis for Java Bytecode

Non-termination analysis proves that programs, or parts of a program, do not terminate. This is important since non-termination is often an unexpected behaviour of computer programs and exposes a bug in their code. While research has found ways of proving non-termination of logic programs and of term rewriting systems, this is hardly the case for imperative programs. In this paper, we describe and experiment with a technique for proving non-termination of imperative, bytecode programs by relating their non-termination to that of a (constraint) logic program. Moreover, we show that our non-termination test effectively helps a termination test, by avoiding expensive search for termination proofs of those portions of the code where such proofs do not exist.

A non-termination criterion for binary constraint logic programs

AbstractOn the one hand, termination analysis of logic programs is now a fairly established research topic within the logic programming community. On the other hand, non-termination analysis seems to remain a much less attractive subject. If we divide this line of research into two kinds of approaches, dynamic versus static analysis, this paper belongs to the latter. It proposes a criterion for detecting non-terminating atomic queries with respect to binary constraint logic programming (CLP) rules, which strictly generalizes our previous works on this subject. We give a generic operational definition and an implemented logical form of this criterion. Then we show that the logical form is correct and complete with respect to the operational definition.

Nontermination inference of logic programs

We present a static analysis technique for nontermination inference of logic programs. Our framework relies on an extension of the subsumption test, where some specific argument positions can be instantiated while others are generalized. We give syntactic criteria to statically identify such argument positions from the text of a program. Atomic left looping queries are generated bottom-up from selected subsets of the binary unfoldings of the program of interest. We propose a set of correct algorithms for automating the approach. Then, nontermination inference is tailored to attempt proofs of optimality of left termination conditions computed by a termination inference tool. An experimental evaluation is reported and the analyzers can be tried online at http://www.univ-reunion.fr/~gcc. When termination and nontermination analysis produce complementary results for a logic procedure, then with respect to the leftmost selection rule and the language used to describe sets of atomic queries, each analysis is optimal and together, they induce acharacterizationof the operational behavior of the logic procedure.