Meta-level “Change-Design” Instruments for Enhanced Software Changeability during Evolution

The central theme of this paper is enhancing the visibility of changes in order to retain good structure, simplicity and changeability of an evolving software system. Other related practical problems addressed in the paper are avoiding explosion of similar component versions, dealing with the impact of multiple changes affecting software during evolution, and reuse of features across system releases, while also allowing each system release to evolve in own direction, interpedently of other releases. We point to certain difficulties to address the above problems with conventional “design for change” and Software Configuration Management techniques. We then propose to alleviate the problems with meta-level extensions to conventional techniques. The proposed approach is based on separation of change specifications (contained in meta-level structures) from architectureand implementation-level program structures of an evolving system. In short-term, our approach eases day-to-day maintenance. In long-term, the approach provides means to unify similar evolution patterns with metalevel generics, helping us address the above mentioned evolution problems. By “similar evolution patterns” we mean both similar patterns of change specifications, as well as similarities among system components affected by changes. The approach paves the way to reuse-based evolution in which we manage multiple versions of a software system released to customers from a core of generic, reusable software representations.