Measuring the Strength of Indirect Coupling

It is widely accepted that coupling plays an important role in software quality, particularly in the areas of software maintenance, so effort should be made to keep coupling levels to a minimum in order to reduce the complexity of the system. We have previously introduced the concept of "indirect" coupling - coupling formed by relationships/dependencies that are not directly evident - with the belief that high levels of indirect coupling can constitute greater costs to maintenance as it is harder to detect. In this paper we extend our previous studies by proposing metrics that can advance our understanding of the exact relationship between indirect coupling and maintainability. In particulars the metrics focus on the reflection of "strength" as it is a fundamental component of coupling. We present our observations on the results of applying the metrics to existing Java applications.