Soft constraint abstraction based on semiring homomorphism

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Journal Article
Theoretical Computer Science, 2008, 403 (2-3), pp. 192 - 201
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The semiring-based constraint satisfaction problems (semiring CSPs), proposed by Bistarelli, Montanari and Rossi [S. Bistarelli, U. Montanari, F. Rossi, Semiring-based constraints solving and optimization, Journal of the ACM 44 (2) (1997) 201-236], is a very general framework of soft constraints. In this paper we propose an abstraction scheme for soft constraints that uses semiring homomorphism. To find optimal solutions of the concrete problem, we first work in the abstract problem and find its optimal solutions, and then use them to solve the concrete problem. In particular, we show that a mapping preserves optimal solutions if and only if it is an order-reflecting semiring homomorphism. Moreover, for a semiring homomorphism α and a problem P over S, if t is optimal in α (P), then there is an optimal solution over(t, ̄) of P such that over(t, ̄) has the same value as t in α (P). © 2008 Elsevier B.V. All rights reserved.
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