Salvador Abreu, Lu s Moniz Pereira, and Philippe Codognet. Improving backward execution in the andorra family of languages. In Proceedings of the International Joint Conference and Symposium on Logic Programming. MIT Press, 1992.  @ NUS  Home/Search   Document Details and Download   Summary   Related Articles   Check

....situations of unsatisfiability again, everywhere and as soon as possible, modulo the other factors allowing an efficient branching rule to be obtained. This can be done by selecting with a higher priority the literals occurring in these clauses. A similar method had been proposed by Abreu et al. [1] for improving the execution of non deterministic concurrent logic languages. This idea can be simply realized by adding a weight c to each clause. Each time DPLL selects a propositional variable that would immediately lead to inconsistency, each initial clause c of the SAT instance that would ....

S. Abreu, L. M. Pereira and P. Codognet. Improving Backward Execution in the Andorra Family of Languages. In Proceedings of the Joint International Conference and Symposium on Logic Programming, (JICSLP'92), pages 384-- 398, November, 1992.

....presented here extend this optimization to allow reordering of arbitrary goals. Our third application is intelligent backtracking. This can improve efficiency by avoiding reexecution of goals (and, therefore, constraint satisfaction operations) which have no relation with the failure being handled [1]. In addition to these applications, constraint independence has another area of application which is quite specific to CLP. The idea is to decompose the single constraint solver into a number of constraint solvers each processing independent sequences of constraints. This is useful because ....

S. Abreu, L. Pereira, and P. Codognet. Improving Backward Execution in the Andorra Family of Languages. In 1992 Joint International Conference and Symposium on Logic Programming, pages 369--384. MIT Press, November 1992.

....by step 2. Should the instance ACR be of the form AGENT = ARG, where ARG is a class member name, it will be evaluated before step 2, leading to a more optimized query in the sense that it will only produce solutions which satisfy the ACR. This approach is similar to the Andorra Principle [4], also known as sidetracking , which consists in reordering goals so as to evaluate the determinate ones first. 4. Should there be a second tuple specified in the operation, as is the case for the modify operation, the instance ACR is evaluated again, before the modifying part of the clause, ....

Salvador Abreu, Lu s Moniz Pereira, and Philippe Codognet. Improving backward execution in the andorra family of languages. In Proceedings of the International Joint Conference and Symposium on Logic Programming. MIT Press, 1992.

....it is, because both search space narrowing techniques built into the AKL model rely exclusively on forward execution, not on any knowledge of whatever occurred during backward execution, especially the information conveyed by the occurrence of failures. Our previous work in this direction (see [1, 2]) shows that there is a non negligible gain to be obtained from the failure information, even with simple minded heuristics. Our present work explores techniques for pruning the search space so as to obtain consistent e ective speedups for combinatorial problems, while retaining an execution ....

....problems, while retaining an execution eciency close to that of the original system. To achieve this we propose to make use of binding dependency information to guide the unfolding of an AKL computation. One way this is accomplished is by improving the accuracy of the methods explored in [2]. The basic problem of intelligent backtracking (IB) in Prolog (see [4, 6] is to locate the bindings responsible for the occurrence of a failure, and backtrack directly to their originator, designated as the culprit, so that unnecessary work (i.e. irrelevant to the con ict) is eschewed. To do so, ....

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Salvador Abreu, Lus Moniz Pereira, and Philippe Codognet. Improving backward execution in the andorra family of languages. In Apt [3], pages 384-398.

....Both or parallelism, and and parallelism between non determinate (and determinate) goals can be exploited. Moreover, the search space can be much reduced over traditional Prolog systems. Further improvements to AKL s search rule have been performed by Abreu, Pereira and Codognet [APC92a] The authors have studied failure driven configuration reordering, which can be seen as an application of the first fail principle to the unfolding of an AKL computation. This shows that And Or tree Rewriting systems (AORS) which encompasses both AKL and the EAM, provide a fertile base for the ....

Salvador Abreu, Lu'is Moniz Pereira, and Philippe Codognet. Improving backward execution in the andorra family of languages. In Krzysztof Apt, editor, Proceedings of the Joint International Conference and Symposium on Logic Programming, pages 384--398, Washington, USA, 1992. The MIT Press.

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