An Empirical Investigation of Modularity Metrics for Indicating Architectural Technical Debt

Architectural technical debt (ATD) is incurred by design decisions that consciously or unconsciously compromise system-wide quality attributes, particularly maintainability and evolvability. ATD needs to be identified and measured, so that it can be monitored and eventually repaid, when appropriate. In practice, ATD is difficult to identify and measure, since ATD does not yield observable behaviors to end users. One indicator of ATD, is the average number of modified components per commit (ANMCC): a higher ANMCC indicates more ATD in a software system. However, it is difficult and sometimes impossible to calculate ANMCC, because the data (i.e., the log of commits) are not always available. In this work, we propose to use software modularity metrics, which can be directly calculated based on source code, as a substitute of ANMCC to indicate ATD. We validate the correlation between ANMCC and modularity metrics through a holistic multiple case study on thirteen open source software projects. The results of this study suggest that two modularity metrics, namely Index of Package Changing Impact (IPCI) and Index of Package Goal Focus (IPGF), have significant correlation with ANMCC, and therefore can be used as alternative ATD indicators. Copyright © 2014 ACM 978-1-4503-2577-6/14/06 ...$15.00