Using pivot consistency to decompose and solve functional CSPS

  • Authors:
  • Philippe David

  • Affiliations:
  • LIRMM, (UMR C9928 CNRS/Université Montpellier II), Montpellier Cedex 5, France

  • Venue:
  • Journal of Artificial Intelligence Research
  • Year:
  • 1995

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Abstract

Many studies have been carried out in order to increase the search efficiency of constraint satisfaction problems; among them, some make use of structural properties of the constraint network; others take into account semantic properties of the constraints, generally assuming that all the constraints possess the given property. In this paper, we propose a new decomposition method benefiting from both semantic properties of functional constraints (not bijective constraints) and structural properties of the network; furthermore, not all the constraints need to be functional. We show that under some conditions, the existence of solutions can be guaranteed. We first characterize a particular subset of the variables, which we name a root set. We then introduce pivot consistency, a new local consistency which is a weak form of path consistency and can be achieved in O(n2d2 complexity (instead of O(n3d3) for path consistency), and we present associated properties; in particular, we show that any consistent instantiation of the root set can be linearly extended to a solution, which leads to the presentation of the aforementioned new method for solving by decomposing functional CSPs.