Constraint-Based Model Refactoring

The UML standard specifies well-formedness rules as constraints on UML models. To be correct, refactoring of a model must take these constraints into account and check that they are still satisfied after a refactoring has been performed - if not, the refactoring must be refused. With constraint-based refactoring, constraint checking is replaced by constraint solving, lifting the role of constraints from permitting or denying a tentative refactoring to computing additional model changes required for the refactoring to be executable. Thus, to the degree that the semantics of a modelling language is specified using constraints, refactorings based on these constraints are guaranteed to be meaning preserving. To enable the reuse of pre-existing constraints for refactoring, we present a mapping from well-formedness rules as provided by the UML standard to constraint rules as required by constraint-based refactoring. Using these mappings, models can be refactored at no extra cost; if refactorings fail, the lack of meaning preservation points us to how the constraint-based semantic specifications of the modelling language can be improved.