How do OSS projects change in number and size? A large-scale analysis to test a model of project growth

摘要

Established Open Source Software (OSS) projects can grow in size if newdevelopers join, but also the number of OSS projects can grow if developerschoose to found new projects. We discuss to what extent an established modelfor firm growth can be applied to the dynamics of OSS projects. Our analysis isbased on a large-scale data set from SourceForge (SF) consisting of monthlydata for 10 years, for up to 360'000 OSS projects and up to 340'000 developers.Over this time period, we find an exponential growth both in the number ofprojects and developers, with a remarkable increase of single-developerprojects after 2009. We analyze the monthly entry and exit rates for bothprojects and developers, the growth rate of established projects and themonthly project size distribution. To derive a prediction for the latter, weuse modeling assumptions of how newly entering developers choose to eitherfound a new project or to join existing ones. Our model applies only tocollaborative projects that are deemed to grow in size by attracting newdevelopers. We verify, by a thorough statistical analysis, that the Yule-Simondistribution is a valid candidate for the size distribution of collaborativeprojects except for certain time periods where the modeling assumptions nolonger hold. We detect and empirically test the reason for this limitation,i.e., the fact that an increasing number of established developers foundadditional new projects after 2009.