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International Conference on Principles and Practice of Constraint Programming

CP 1996: Principles and Practice of Constraint Programming — CP96 pp 1–15Cite as

On confluence of Constraint Handling Rules

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Part of the book series: Lecture Notes in Computer Science ((LNCS,volume 1118))

Abstract

We introduce the notion of confluence for Constraint Handling Rules (CHR), a powerful language for writing constraint solvers. With CHR one simplifies and solves constraints by applying rules. Confluence guarantees that a CHR program will always compute the same result for a given set of constraints independent of which rules are applied. We give a decidable, sufficient and necessary syntactic condition for confluence.

Confluence turns out to be an essential syntactical property of CHR programs for two reasons. First, confluence implies correctness (as will be shown in this paper). In a correct CHR program, application of CHR rules preserves logical equivalence of the simplified constraints. Secondly, even when the program is already correct, confluence is highly desirable. Otherwise, given some constraints, one computation may detect their inconsistency while another one may just simplify them into a still complex constraint.

As a side-effect, the paper also gives soundness and completeness results for CHR programs. Due to their special nature, and in particular correctness, these theorems are stronger than what holds for the related families of (concurrent) constraint programming languages.

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Author information

Authors and Affiliations

  1. Computer Science Department, University of Munich, Oettingenstr. 67, 80538, Munich, Germany

    Slim Abdennadher, Thom Frühwirth & Holger Meuss

Authors
  1. Slim Abdennadher
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  2. Thom Frühwirth
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  3. Holger Meuss
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Editor information

Eugene C. Freuder

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© 1996 Springer-Verlag Berlin Heidelberg

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Abdennadher, S., Frühwirth, T., Meuss, H. (1996). On confluence of Constraint Handling Rules. In: Freuder, E.C. (eds) Principles and Practice of Constraint Programming — CP96. CP 1996. Lecture Notes in Computer Science, vol 1118. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-61551-2_62

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  • DOI: https://doi.org/10.1007/3-540-61551-2_62

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  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-540-61551-4

  • Online ISBN: 978-3-540-70620-5

  • eBook Packages: Springer Book Archive

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