Coevolution Index: A Metric for Tracking Evolutionary Coupling

This paper proposes a new metric, namely the coevolution index (CEI), for measuring the relative evolutionary coupling of modules of a software system. CEI is inspired by the h-index, which is a popular metric used for measuring the productivity and citation impact of scholars and scientists. CEI of a module is equal to n, which is the number of times it is modified together with at least n other modules of the system. We develop a script that can calculate CEI for source files in a code repository. We analyze the repository of 4 software systems. Source files that are subject to a high number of changes to address issues tend to have high CEI scores. CEI also reflects a relative footprint in maintenance efforts by definition. Hence, it can help in tracking technical debt interest and focusing the refactoring efforts for improving maintainability and reusability.