Evolution Styles - Formal foundations and tool support for software architecture evolution

Architecture evolution is a central feature of virtually all software systems. As new market opportunities, technologies, platforms, and frameworks become available systems must change their organizational structures to accommodate them, requiring large-scale and systematic restructuring. Today architects have few tools to help them plan and execute such evolutionary paths. In particular, they have almost no assistance in reasoning about questions such as: How should we stage the evolution to achieve business goals in the presence of limited development resources? How can we reduce risk in incorporating new technologies and infrastructure required by the target architecture? How can we make principled tradeoffs between time and development effort? What kinds of changes can be made independently, and which require coordinated system-wide modifications? How can an evolution plan be represented and communicated within an organization? In this report we outline first steps towards a formal basis for assisting architects in developing and reasoning about architectural evolution paths. The key insight behind the approach is that at an architectural level of abstraction many system evolutions follow certain common patterns – or evolution styles. By taking advantage of regularity in the space of common architectural evolutions, and by making the notion of evolutions styles a first-class entity that can be formally defined, we can provide automated assistance for expressing architecture evolution, and for reasoning about both the correctness and quality of evolution paths. This research has benefited from a discussion of Architecture Evolution with the members of the ABLE research group (Jeff Barnes, Roni Burd, Orieta Celiku, Owen Cheng, George Fairbanks, Jung Soo Kim, Vahe Poladian, and Bradley Schmerl); members of the SEI SAT initiative who participated in a joint reading group on this topic (Ipek Ozkaya and Mark Klein). I would also like to acknowledge Sungwon Kang and Dalila Tamzalit, who have sparked many useful insights about the topic of Architectural Evolution.