An empirical study of architectural change in open-source software systems

From its very inception, the study of software architecture has recognized architectural decay as a regularly occurring phenomenon in long-lived systems. Architectural decay is caused by repeated changes to a system during its lifespan. Despite decay's prevalence, there is a relative dearth of empirical data regarding the nature of architectural changes that may lead to decay, and of developers' understanding of those changes. In this paper, we take a step toward addressing that scarcity by conducting an empirical study of changes found in software architectures spanning several hundred versions of 14 open-source systems. Our study reveals several new findings regarding the frequency of architectural changes in software systems, the common points of departure in a system's architecture during maintenance and evolution, the difference between system-level and component-level architectural change, and the suitability of a system's implementation-level structure as a proxy for its architecture.