Contractibility and Contractible Approximations of Soft Global Constraints

Michael J. Maher
We study contractibility and its approximation for two very general classes of soft global constraints. We introduce a general formulation of decomposition-based soft constraints and provide a sufficient condition for contractibility and an approach to approximation. For edit-based soft constraints, we establish that the tightest contractible approximation cannot be expressed in edit-based terms, in general.