Beyond depth-first strategies: improving tabled logic programs through alternative scheduling

Publication Type Journal Article
School or College College of Engineering
Department Computing, School of
Creator Freire, Juliana
Other Author Swift, Terrance; Warren, David S.
Title Beyond depth-first strategies: improving tabled logic programs through alternative scheduling
Date 1998
Description Tabled evaluation ensures termination for programs with finite models by keeping track of which subgoals have been called. Given several variant subgoals in an evaluation, only the fi rst one encountered will use program-clause resolution; the rest will resolve with the answers generated by the first subgoal. This use of answer resolution prevents infi nite looping that sometimes happens in SLD. Because answers that are produced in one path of the computation may be consumed, asynchronously, in others, tabling systems face an important scheduling choice not present in traditional top-down evaluation: when to schedule answer resolution. This paper investigates alternate scheduling strategies for tabling in a WAM implementation, the SLG-WAM. The original SLG-WAM had a simple mechanism for scheduling answer resolution that was expensive in terms of trailing and choice-point creation. We propose here a more sophisticated scheduling strategy, batched scheduling, which reduces the overheads of these operations and provides dramatic space reduction as well as speedups for many programs. We also propose a second strategy, local scheduling, which has applications to nonmonotonic reasoning, and when combined with answer subsumption, can arbitrarily improve the performance of some programs.
Type Text
Publisher MIT Press
First Page 1
Last Page 39
Subject Alternate scheduling; SLG-WAM; Tabled logic programs
Subject LCSH Logic programming; Computer scheduling
Language eng
Bibliographic Citation Freire, J., Swift, T., & Warren, D. S. (1998). Beyond depth-first strategies: improving tabled logic programs through alternative scheduling. Journal of Functional and Logic Programming, 3, April, 1-39.
Rights Management (c) MIT Press http://mitpress.mit.edu/
Format Medium application/pdf (portable document)
Format Extent 252,108 bytes
Identifier ir-main,12383
ARK ark:/87278/s6kw606q
ID 702791
setname ir_uspace
Reference URL https://collections.lib.utah.edu/details?id=702791
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