Modelling Soft Constraints: A Survey

Constraint programming is an approach for solving (mostly combinatorial) problems by stating constraints over the problem variables. In some problems, there is no solution satisfying all the constraints or the problem formulation must deal with uncertainty, vagueness, or imprecision. In such a case the standard constraint satisfaction techniques dealing with hard constraints cannot be used directly and some form of soft constraints is required. In the paper we survey four generic models for soft constraints, namely hierarchical, partial, valued, and semiring-based constraint satisfaction.