An Architectural Approach to Software Evolution and Integration

As time passes, software systems need to be maintained, modified, and integrated with other systems so as not to age and become obsolete. In the present thesis, we investigate how the concepts of software components and software architecture can be used to facilitate software evolution and integration. Based on three case studies, we argue that considering a software system at a high abstraction level, as a set of connected components, makes possible a cost efficient and structured evolution and integration process. The systems in two of our case studies are information systems developed in-house used for managing and manipulating business-critical data. The third case study concerns an integration framework in which systems can be integrated without modification. In the thesis, we describe how several architectural alternatives can be developed based on architectural descriptions of existing systems, and how these can be evaluated regarding a number of concerns in a relatively rapid way, while achieving an acceptable confidence/effort ratio. We describe how some of these concerns can be addressed in more detail, namely maintainability, cost of implementation, and time of implementation; we also discuss the risk involved in the decision. We show how although the existing architecture may reflect insufficient design decisions and an outdated state of practice, it can and should be seen as a prototype revealing strengths that should be preserved and weaknesses that should be addressed during redesign. We also describe four different integration approaches and the feasibility of each under various circumstances: Enterprise Application Integration (EAI), interoperability through import and export facilities, integration at data level, and integration at source code level. The two last of these are compared in more detail, revealing that code level integration is more risky but not necessarily more costly than data level integration, but is advantageous from a technical perspective.