Observable Confluence for Constraint Handling Rules

  • Gregory J. Duck
  • Peter J. Stuckey
  • Martin Sulzmann
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4670)


Constraint Handling Rules (CHR) are a powerful rule based language for specifying constraint solvers. Critical for any rule based language is the notion of confluence, and for terminating CHR programs there is a decidable test for confluence. But many CHR programs that are in practice confluent fail this confluence test. The problem is that the states that illustrate non-confluence are not observable from the initial goals of interest. In this paper we introduce the notion of observable confluence, a more general notion of confluence which takes into account whether states are observable. We devise a test for observable confluence which allows us to verify observable confluence for a range of CHR programs dealing with agents, type systems, and the union-find algorithm.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2007

Authors and Affiliations

  • Gregory J. Duck
    • 1
  • Peter J. Stuckey
    • 1
  • Martin Sulzmann
    • 2
  1. 1.NICTA Victoria Laboratory, Department of Computer Science and Software Engineering, University of Melbourne, 3010Australia
  2. 2.School of Computing, National University of Singapore, S16 Level 5, 3 Science Drive 2,117543Singapore

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