Contractibility for open global constraints

Open forms of global constraints allow the addition of new variables to an argument during the execution of a constraint program. Such forms are needed for difficult constraint programming problems, where problem construction and problem solving are interleaved, and fit naturally within constraint l...

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Bibliographic Details
Published in:Theory and practice of logic programming Vol. 17; no. 4; pp. 365 - 407
Main Author: MAHER, MICHAEL J.
Format: Journal Article
Language:English
Published: Cambridge, UK Cambridge University Press 01.07.2017
Subjects:
Constraints
Logic programming
Problem solving
Regular Papers
global constraints
soft constraints
open constraints
ISSN:1471-0684, 1475-3081
Online Access:Get full text
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Summary:Open forms of global constraints allow the addition of new variables to an argument during the execution of a constraint program. Such forms are needed for difficult constraint programming problems, where problem construction and problem solving are interleaved, and fit naturally within constraint logic programming. However, in general, filtering that is sound for a global constraint can be unsound when the constraint is open. This paper provides a simple characterization, called contractibility, of the constraints, where filtering remains sound when the constraint is open. With this characterization, we can easily determine whether a constraint has this property or not. In the latter case, we can use it to derive a contractible approximation to the constraint. We demonstrate this work on both hard and soft constraints. In the process, we formulate two general classes of soft constraints.
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ISSN:1471-0684
1475-3081
DOI:10.1017/S1471068417000126