Exploiting Unfounded Sets for HEX-Program Evaluation

  • Thomas Eiter
  • Michael Fink
  • Thomas Krennwallner
  • Christoph Redl
  • Peter Schüller
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 7519)


HEX programs extend logic programs with external computations through external atoms, whose answer sets are the minimal models of the Faber-Leone-Pfeifer-reduct. As already reasoning from Horn programs with nonmonotonic external atoms of polynomial complexity is on the second level of the polynomial hierarchy, answer set checking needs special attention; simply computing reducts and searching for smaller models does not scale well. We thus extend an approach based on unfounded sets to HEX and integrate it in a Conflict Driven Clause Learning framework for HEX program evaluation. It reduces the check to a search for unfounded sets, which is more efficiently implemented as a SAT problem. We give a basic encoding for HEX and show optimizations by additional clauses. Experiments show that the new approach significantly decreases runtime.


Answer Set Programming Nonmonotonic Reasoning Unfounded Sets FLP Semantics 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  • Thomas Eiter
    • 1
  • Michael Fink
    • 1
  • Thomas Krennwallner
    • 1
  • Christoph Redl
    • 1
  • Peter Schüller
    • 1
  1. 1.Institut für InformationssystemeTechnische Universität WienViennaAustria

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