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

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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: improving tabled logic programs through alternative scheduling strategies
Date 1996
Description Tabled evaluations ensure termination of logic programs with fi nite 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 uses answer resolution This use of answer resolution prevents infi nite looping which happens in SLD Given the asynchronicity of answer generation and answer return, tabling systems face an important scheduling choice not present in traditional top-down evaluation How does the order of returning answers to consuming subgoals affect program efficiency This paper investigates alternate scheduling strategies for tabling in a WAM implementation, the SLG-WAM. The original SLG-WAM had a simple mechanism of scheduling answers to be returned to callers which 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 non-monotonic reasoning and when combined with answer subsumption can improve the performance of some programs by arbitrary amounts.
Type Text
Publisher Springer
First Page 1
Last Page 14
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. (1996). Beyond depth-first: improving tabled logic programs through alternative scheduling strategies. Proceedings PLILP, 1-14.
Rights Management © Springer (The original publication is available at www.springerlink.com)
Format Medium application/pdf
Format Extent 886,587 bytes
Identifier ir-main,12391
ARK ark:/87278/s6sf3d7c
Setname ir_uspace
ID 702423
Reference URL https://collections.lib.utah.edu/ark:/87278/s6sf3d7c