Software Architecture Evolution through Evolvability Analysis

In this thesis, we study evolution of software architecture and investigate ways to support this evolution. The central theme of the thesis is how to analyze software evolvability, i.e., a system’s ability to easily accommodate changes. We focus on two main aspects: (i) what software characteristics are necessary for an evolvable software system; and (ii) how to assess evolvability of long-lived proprietary systems in a systematic manner. A secondary focus is to investigate how evolvability is addressed in open source software evolution. We have performed a systematic review of architecture evolution research, and proposed a software evolvability model, in which subcharacteristics of software evolvability and corresponding measuring attributes are identified. Based on this model, we have proposed the softwarearchitectureevolvabilityanalysis (AREA) process which provides repeatable techniques for supporting software architecture evolution: a) Qualitative evolvability analysis method that focuses on improving the capability of being able to understand and analyze systematically the impact of change stimuli on software architecture evolution; b) Quantitative evolvability analysis method that provides quantifications of stakeholders’ evolvability concerns and potential architectural solutions’ impacts on evolvability. These techniques have been validated in industrial settings of different domains, and can be used as an integral part of software development and evolution process. This is to ensure that the implications of the potential improvement strategies and evolution path of software architectures are analyzed with respect to the evolvability subcharacteristics. As a supplementary research contribution, we have conducted a systematic review of the existing studies in open source software (OSS) evolution, and performed a comprehensive analysis which describes how software evolvability is addressed during the development and evolution of OSS, and identified challenges and future research directions in OSS evolution