Object-oriented design patterns and high-level refactorings are popular means of implementing and evolving large object-oriented software systems. Unfortunately, these techniques are inadequately supported at implementation level by current-day software development environments. To alleviate this problem, we propose to use the promising technique of declarative metaprogramming. It offers a tight, yet flexible, symbiosis between a base language and a metalevel declarative reasoning engine. It provides a uniform and language-independent way to specify design patterns and transformations declaratively, to instantiate patterns and generate code for them, and to deal with the evolution of these pattern instances. Providing support for evolution of a software system in terms of the design pattern instances it uses is the main emphasis of this paper. 1.