A Filtering Algorithm For Constraints Of Difference In CSPs

Abstract

Many real-life Constraint Satisfaction Problems (CSPs) involve some constraints similar to the alldifferent constraints. These constraints are called constraints of difference. They are defined on a subset of variables by a set of tuples for which the values occuring in the same tuple are all different. In this paper, a new filtering algorithm for these constraints is presented. It achieves the generalized arc-consistency condition for these non-binary constraints. It is based on matching theory and its complexity is low. In fact, for a constraint defined on a subset of p variables having domains of cardinality at most d, its space complexity is OCpd) and its time complexity is O(p2d2). This filtering algorithm has been successfully used in the system RESYN (Vismara et al. 1992), to solve the subgraph isomorphism problem.