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Transformation-based bottom-up computation of the well-founded model

  • Stefan Brass
  • Ulrich Zukowski
  • Burkhard Freitag
Computation
Part of the Lecture Notes in Computer Science book series (LNCS, volume 1216)

Abstract

We present a bottom-up algorithm for the computation of the well-founded model of non-disjunctive logic programs. Our method is based on the elementary program transformations studied by Brass and Dix [6, 7]. However, their “residual program” can grow to exponential size, whereas for function-free programs our “program remainder” is always polynomial in the size, i.e. the number of tuples, of the extensional database (EDB). As in the SLG-resolution of Chen and Warren [11, 12, 13], we do not only delay negative but also positive literals if they depend on delayed negative literals. When disregarding goal-directedness, which needs additional concepts, our approach can be seen as a simplified bottom-up version of SLG-resolution applicable to range-restricted Datalog programs. Since our approach is also closely related to the alternating fixpoint procedure [27, 28], it can possibly serve as a basis for an integration of the resolution-based, fixpoint-based, and transformation-based evaluation methods.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1997

Authors and Affiliations

  • Stefan Brass
    • 1
  • Ulrich Zukowski
    • 2
  • Burkhard Freitag
    • 2
  1. 1.Institut für InformatikUniversität HildesheimHildesheimGermany
  2. 2.Fakultät für Mathematik und InformatikUniversität PassauPassauGermany

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