Abstract.With the increased interest in refactoring, UML tool vendors seek ways to support software developers in applying a (sequence of) refactoring(s). The problem with such tools is that the UML metamodel -on which their repository is based -is inadequate to maintain the consistency between the model and the code while one of them gets refactored. Therefore, we propose a set of minimal extensions to the UML metamodel, which is sufficient to reason about refactoring for all common OO languages. For instance, by specifying pre-and postconditions in OCL, we are able to compose primitive refactorings, verify preservation of program behavior, and trigger refactorings based on code smells. This way, we provide future MDA tools with the ability to improve existing UML designs, yet keeping them in synch with the underlying code base.

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