The FreeBSD Project: A Replication Case Study of Open Source Development

Case studies can help to validate claims that open source software development produces higher quality software at lower cost than traditional commercial development. One problem inherent in case studies is external validity—we do not know whether or not results from one case study apply to another development project. We gain or lose confidence in case study results when similar case studies are conducted on other projects. This case study of the FreeBSD project, a long-lived open source project, provides further understanding of open source development. The paper details a method for mining repositories and querying project participants to retrieve key process information. The FreeBSD development process is fairly well-defined with proscribed methods for determining developer responsibilities, dealing with enhancements and defects, and managing releases. Compared to the Apache project, FreeBSD uses 1) a smaller set of core developers—developers who control the code base—that implement a smaller percentage of the system, 2) a larger set of top developers to implement 80 percent of the system, and 3) a more well-defined testing process. FreeBSD and Apache have a similar ratio of core developers to people involved in adapting and debugging the system and people who report problems. Both systems have similar defect densities and the developers are also users in both systems.