Retroactive Subsumption-Based Tabled Evaluation of Logic Programs

Flávio Cruz and Ricardo Rocha

September 2010

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Abstract

Tabled evaluation is a recognized and powerful implementation technique that overcomes some limitations of traditional Prolog systems in dealing with recursion and redundant sub-computations. Tabling based systems use call similarity to determine if a tabled subgoal will produce their own answers or if it will consume from another subgoal. While call variance has been a very popular approach, call subsumption can yield superior time performance and space improvements as it allows greater reuse of answers. However, the call order of the subgoals can greatly affect the success and applicability of the call subsumption technique. In this work, we present an extension, named Retroactive Call Subsumption, that supports call subsumption by allowing full sharing of answers between subsumed/subsuming subgoals, independently on the order in which they are called. Our experiments using the YapTab tabling engine show considerable gains in evaluation time for some applications, at the expense of a very small overhead for the programs that cannot benefit from it.

Bibtex

@InProceedings{cruz-jelia10,
  author =    {F. Cruz and R. Rocha},
  title =     {{Retroactive Subsumption-Based Tabled Evaluation of Logic Programs}},
  booktitle = {Proceedings of the 12th European Conference on Logics in Artificial Intelligence (JELIA 2010)},
  pages =     {130--142},
  number =    {6341},
  series =    {LNAI},
  publisher = {Springer},
  editor =    {T. Janhunen and I. Niemelä},
  month =     {September},
  year =      {2010},
  address =   {Helsinki, Finland},
}

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