The unified extensional versioning model

Versioning of components in a system is a well-researched field where various adequate techniques have already been established. In this paper, we look at how versioning can be extended to cover also the structural aspects of a system. There exist two basic techniques for versioning - intentional and extensional - and we propose a unified extensional versioning model for versioning of both components and structure in the same way. The unified model is described in detail and three different policies that can be implemented on top of the general model are exemplified/illustrated by three prototype tools constructed by the authors. The model is analysed with respect to the number of versions and con- figurations it generates and has to manage. Finally, the unified extensional model is compared to more traditional intentional models on some important parameters. The conclusions are that the unified model is indeed viable. It not only pro- vides the functionality offered by the intentional model with respect to flexibility during development and management of combinatoric complexity, but also offers a framework for management of configurations that enables systems to provide much more advanced support than is commonly available.