"May the fork be with you": novel metrics to analyze collaboration on GitHub

Multi-repository software projects are becoming more and more popular, thanks to web-based facilities such as Github. Code and process metrics generally assume a single repository must be analyzed, in order to measure the characteristics of a codebase. Thus they are not apt to measure how much relevant information is hosted in multiple repositories contributing to the same codebase. Nor can they feature the characteristics of such a distributed development process. We present a set of novel metrics, based on an original classification of commits, conceived to capture some interesting aspects of a multi-repository development process. We also describe an efficient way to build a data structure that allows to compute these metrics on a set of Git repositories. Interesting outcomes, obtained by applying our metrics on a large sample of projects hosted on Github, show the usefulness of our contribution.