Turnover is the phenomenon of continuous influx and retreat of human resources in a team. Despite being well-studied in many settings, turnover has not been characterized for open-source software projects. We study the source code repositories of five open-source projects to characterize patterns of turnover and to determine the effects of turnover on software quality. We define the base concepts of both external and internal turnover, which are the mobility of developers in and out of a project, and the mobility of developers inside a project, respectively. We provide a qualitative analysis of turnover patterns. We also found, in a quantitative analysis, that the activity of external newcomers negatively impact software quality.

Context: Ownership metrics measure how the workload of software modules is shared among their developers. They have been shown to be accurate indicators of software quality. Objective: Since ownership metrics studies were done only on industrial software projects, we replicated such a study on Java free/libre and open source software (FLOSS) projects. Our goal was to generalize an "ownership law" that stated that minor developers should be avoided. Method: We explored the relationship between ownership metrics and fault-proneness on seven FLOSS projects, using publicly available corpora to retrieve the fault-related information. Results: In our corpus, the relationship between ownership metrics and module faults is weak. At best, less than half of projects exhibit a significant correlation, and at worst, no projects at all. Moreover, fault-proneness seems to be much more influenced by module size than by ownership. Conclusion: The results of ownership studies done on closed-source projects do not generalize to FLOSS projects. To understand the reasons for that, we performed an in-depth analysis and found that the lack of correlation between ownership metrics and module faults is due to the distributions of contributions among developers and the presence of "heroes" in FLOSS projects.

As Domain-Specific Modeling Languages (DSML) become more widespread, it is now possible for non-computer scientists to design complex systems. Not only do DSMLs make modeling more accessible to domain experts, they also improve their efficiency. Using such models, the problem of their maintenance and evolution arises, with common software engineering issues, such as reversibility and traceability of developments. In this article we present the integration of a collaborative edition process into a model-driven engineering (MDE) simulation platform defining its own DSML, which includes a serialization procedure. Our novel approach defines a collaborative work and version control process. This process uses the concrete textual syntax defined by this DSML, which allows us to use the features of existing Version Control Systems (VCS) to work with serialized models, and helps calculate the differences between two versions of a model, merge versions of these models, and detect merge conflicts.