Investigating whether and how software developers understand open source software licensing

Software provided under open source licenses is widely used, from forming high-profile stand-alone applications (e.g., Mozilla Firefox) to being embedded in commercial offerings (e.g., network routers). Despite the high frequency of use of open source licenses, there has been little work about whether software developers understand the open source licenses that they use. To help understand whether or not developers understand the open source licenses they use, we conducted a survey that posed development scenarios involving three popular open source licenses (GNU GPL 3.0, GNU LGPL 3.0 and MPL 2.0) both alone and in combination. The 375 respondents to the survey, who were largely developers, gave answers consistent with those of a legal expert's opinion in 62% of 42 cases. Although developers clearly understood cases involving one license, they struggled when multiple licenses were involved. To understand the context in which licensing issues arise in practice, we analyzed real-world questions posed by developers about the three licenses considered in the survey on online question-and-answer communities. We also interviewed practicing developers about license interaction problems they have faced. Among several lessons, we learnt that licensing issues can constrain software evolution and that developers are cautious of more restrictive licenses. Our results indicate a need for tool support to help guide developers in understanding the structure of the code and the technical details of a project while taking into account the exact requirements imposed by the licenses involved.