The Eclipse UML2 project has a new feature in the Juno M6 milestone that should help a certain category of applications to keep their UML models in good health. These are UML-based modelling tools that use the EMF Validation Framework for model validation, often because they provide diagram editors based on GMF. The Papyrus project is a good example of such application, and it happens to integrate this new feature.
The UML2 project implements the UML metamodel version 2.4. I have always said that a model is not complete without the constraints that determine what is a well-formed instance. Well, now we can have our diagrams and our constraints, too!