No abstract

The huge quantities of data available in the CVS repositories of large, long-lived libre (free, open source) software projects, and the many interrelationships among those data offer opportunities for extracting large amounts of valuable information about their structure, evolution and internal processes. Unfortunately, the sheer volume of that information renders it almost unusable without applying methodologies which highlight the relevant information for a given aspect of the project. In this paper, we propose the use of a well known set of methodologies (social network analysis) for characterizing libre software projects, their evolution over time and their internal structure. In addition, we show how we have applied such methodologies to real cases, and extract some preliminary conclusions from that experience.

Abstract

In general it is assumed that a software product evolves within the authoring company or group of developers that develop the project. However, in some cases different groups of developers make the software evolve in different directions, a situation which is commonly known as a fork. In the case of free software, although forking is a practice that is considered as a last resort, it is inherent to the four freedoms. This paper tries to shed some light on the practice of forking. Therefore, we have identified significant forks, several hundreds in total, and have studied them in depth. Among the issues that have been analyzed for each fork is the date when the forking occurred, the reason of the fork, and the outcome of the fork, i.e., if the original or the forking project are still developed. Our investigation shows, among other results, that forks occur in every software domain, that they have become more frequent in recent years, and that very few forks merge with the original project.

Software evolution studies have traditionally focused on individual products. In this study we scale up the idea of software evolution by considering software compilations composed of a large quantity of independently developed products, engineered to work together. With the success of libre (free, open source) software, these compilations have become common in the form of 'software distributions', which group hundreds or thousands of software applications and libraries into an integrated system. We have performed an exploratory case study on one of them, Debian GNU/Linux, finding some significant results. First, Debian has been doubling in size every 2 years, totalling about 300 million lines of code as of 2007. Second, the mean size of packages has remained stable over time. Third, the number of dependencies between packages has been growing quickly. Finally, while C is still by far the most commonly used programming language for applications, use of the C++, Java, and Python languages have all significantly increased. The study helps not only to understand the evolution of Debian, but also yields insights into the evolution of mature libre software systems in general.