Sound Object Model Refactorings

Refactorings are usually proposed in an ad hoc way because it is hard to guarantee their soundness with respect to a formal semantics. Usually, even using refactoring tools, developers have to rely on compilation and tests in order to improve their confidence that semantics is preserved, which may not be satisfactory to critical software development. We propose a set of semantics-preserving transformations based on a refinement theory that we propose for Alloy. This set of transformations is shown to be relatively complete in the sense that it can derive a representative set of model transformations, and proven sound with respect to a formal semantics for Alloy in a theorem prover. Moreover, we show how they can be composed to derive refactorings and optimizations. They are a powerful tool for reasoning about object model transformations, and can be used to improve refactoring tools.