Evolution and growth in large libre software projects

Software evolution research has recently focused on new development paradigms, studying whether laws found in more classic development environments also apply. Previous works have pointed out that at least some laws seem not to be valid for these new environments and even Lehman has labeled those (up to the moment few) cases as anomalies and has suggested that further research is needed to clarify this issue. In this line, we consider in this paper a large set of libre (free, open source) software systems featuring a large community of users and developers. In particular, we analyze a number of projects found in literature up to now, including the Linux kernel. For comparison, we include other libre software kernels from the BSD family, and for completeness we consider a wider range of libre software applications. In the case of Linux and the other operating system kernels we have studied growth patterns also at the subsystem level. We have observed in the studied sample that super-linearity occurs only exceptionally, that many of the systems follow a linear growth pattern and that smooth growth is not that common. These results differ from the ones found generally in classical software evolution studies. Other behaviors and patterns give also a hint that development in the libre software world could follow different laws than those known, at least in some cases.