Refactoring of Statecharts

Statecharts are an important tool for specifying the behavior of reactive systems, and development tools can automatically generate object-oriented code from them. As the system is refactored, it is necessary to modify the associated statecharts as well, performing operations such as grouping or ungrouping states, extracting part of a statechart into a separate class, and merging states and transitions. Refactoring tools embedded in object-oriented development environments are making it much easier for developers to modify their programs. However, tool support for refactoring statecharts does not yet exist. As a result, developers avoid making certain changes that are too difficult to perform manually, even though design quality deteriorates. Methodologically, statecharts were meant to enable a systems engineer to describe a complete system, which would then be refined into a concrete implementation (object-oriented or other). This process is not supported by object-oriented development environments, which force each statechart to be specified as part of a class. Automated tool support for refactoring statecharts will also make this kind of refinement possible. This paper describes a case study that shows the usefulness of refactoring support for statecharts, and presents an initial catalog of relevant refactorings. We show that a top-down refinement process helps identify the tasks and classes in a natural way.