Causes of Architecture Changes: An Empirical Study through the Communication in OSS Mailing Lists

Understanding the causes of architecture changes allows us to devise means to prevent architecture knowledge vaporization and architecture degeneration. But the causes are not always known, especially in open source software (OSS) development. This makes it very hard to understand the underlying reasons for the architecture changes and design appropriate modifications. Architecture information is communicated in development mailing lists of OSS projects. To explore the possibility of identifying and understanding the causes of architecture changes, we conducted an empirical study to analyze architecture information (i.e., architectural threads) communicated in the development mailing lists of two popular OSS projects: Hibernate and ArgoUML, verified architecture changes with source code, and identified the causes of architecture changes from the communicated architecture information. The main findings of this study are: (1) architecture information communicated in OSS mailing lists does lead to architecture changes in code; (2) the major cause for architecture changes in both Hibernate and ArgoUML is preventative changes. (3) more than 45% of architecture changes in both projects happened before the first stable version was released, which indicates that the architectures of the investigated OSS projects are relatively stable after the first stable release. Keywords-architecture change; cause of change; open source software; mailing list; communication