Investigating Evolution in Open Source Software

Lehman’s well-known laws of software evolution have existed since the early 1980’s and although they have been nuanced, augmented and discussed many times since then, software and software development practices have changed dramatically since then, not least due to the rise and popularity of open source software (OSS). OSS is written collaboratively with the process and products publically observable, whereas the original laws were derived based on a very different context. The question then arises if Lehman’s laws apply to modern day OSS software. The GitHub repository is the most comprehensive source of OSS projects and is used here to obtain data on how OSS projects have evolved. This work uses one hundred open source projects hosted on GitHub. Metrics are obtained via the provided API, using a purpose-built workbench and several of Lehman’s laws are evaluated using the data available. Coupled with a critique of how judgements can be made from the data available, the study has discovered that the evidence does not support many of the laws. An important proviso with such an approach is the limitation on what data can be extracted and/or inferred from the GitHub API. Nonetheless, there is enough of a challenge made to the laws to warrant further study and a need to revisit some of the laws in the context of open source development.