Technical debt and system architecture: The impact of coupling on defect-related activity

We address this gap by analyzing the relationship between system architecture and maintenance costs for two software systems of similar size, but with very different structures; one has a “Hierarchical” design, the other has a “Core-Periphery” design. We measure the level of system coupling for the 20,000+ components in each system, and use these measures to predict maintenance efforts, or “defect-related activity.” We show that in both systems, the tightly-coupled Core or Central components cost significantly more to maintain then loosely-coupled Peripheral components. In essence, a small number of components generate a large proportion of system costs. However, we find major differences in the potential benefits available from refactoring these systems, related to their differing designs. Our results generate insight into how architectural debt can be assessed by understanding patterns of coupling among components in a system.