An exploratory study of the evolution of software licensing

Free and open source software systems (FOSS) are distributed and made available to users under different software licenses, mentioned in FOSS code by means of licensing statements. Various factors, such as changes in the legal landscape, commercial code licensed as FOSS, or code reused from other FOSS systems, lead to evolution of licensing, which may affect the way a system or part thereof can be subsequently used. Therefore, it is crucial to monitor licensing evolution. However, manually tracking the licensing evolution of thousands of files is a daunting task. After presenting several cases of the effects of licensing evolution, we propose an approach to automatically track changes occurring in the licensing terms of a system. Then, we report an empirical study of the licensing evolution of six different FOSS systems. Results show that licensing underwent frequent and substantial changes.