Who are Source Code Contributors and How do they Change?

Determining who are the copyright owners of a software system is important as they are the individuals and organizations that license the software to its users, and ultimately the legal entities that can enforce its licensing terms and change its license. In this paper we describe the difficulties of identifying the explicit copyright owners of a system, and those who contribute source code to it-who could potentially claim are also copyright owners of it.The paper introduces a method to track the names of contributors, including those explicitly listed as copyright owners from licensing statements in source code file. Then, it reports an empirical study performed on four open source systems-namely ArgoUML, Mozilla, Samba, and Squid-aimed at investigating the characteristics of their contributors and how they relate to the commits recorded in the system and users who perform them (its committers). Results indicate that explicit contributors and copyright owners are not necessarily the most frequent committers. Also, they are often added during larger changes than average.