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Abstract

Loops and the corresponding loop formulas play an important role in answer set programming. On the one hand, they are used for guaranteeing correctness and completeness in SAT-based answer set solvers. On the other hand, they can be used by conventional answer set solvers for finding unfounded sets of atoms. Unfortunately, the number of loops is exponential in the worst case. We demonstrate that not all loops are actually needed for answer set computation. Rather, we characterize the subclass of elementary loops and show that they are sufficient and necessary for selecting answer sets among the models of a program’s completion. Given that elementary loops cannot be distinguished from general ones in atom dependency graphs, we show how the richer graph structure provided by body-head dependency graphs can be exploited for this purpose.

Keywords

Logic Program Dependency Graph Deductive Database Elementary Closure General Loop 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  • Martin Gebser
    • 1
  • Torsten Schaub
    • 1
  1. 1.Institut für InformatikUniversität PotsdamPotsdam

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