Modeling the Centrality of Developer Output with Software Supply Chains

Raw developer output, as measured by the number of changes a developer makes to the system, is simplistic and potentially misleading measure of productivity as new developers tend to work on peripheral and experienced developers on more central parts of the system. In this work, we use Software Supply Chain (SSC) networks and Katz centrality and PageRank on these networks to suggest a more nuanced measure of developer productivity. Our SSC is a network that represents the relationships between developers and artifacts that make up a system. We combine author-to-file, co-changing files, call hierarchies, and reporting structure into a single SSC and calculate the centrality of each node. The measures of centrality can be used to better understand variations in the impact of developer output at Meta. We start by partially replicating prior work and show that the raw number of developer commits plateaus over a project-specific period. However, the centrality of developer work grows for the entire period of study, but the growth slows after one year. This implies that while raw output might plateau, more experienced developers work on more central parts of the system. Finally, we investigate the incremental contribution of SSC attributes in modeling developer output. We find that local attributes such as the number of reports and the specific project do not explain much variation (R-2 = 5.8%). In contrast, adding Katz centrality or PageRank produces a model with an R-2 above 30%. SSCs and their centrality provide valuable insights into the centrality and importance of a developer's work.