An empirical study of slice-based cohesion and coupling metrics

Software reengineering is a costly endeavor, due in part to the ambiguity of where to focus reengineering effort. Coupling and Cohesion metrics, particularly quantitative cohesion metrics, have the potential to aid in this identification and to measure progress. The most extensive work on such metrics is with slice-based cohesion metrics. While their use of semantic dependence information should make them an excellent choice for cohesion measurement, their wide spread use has been impeded in part by a lack of empirical study. Recent advances in software tools make, for the first time, a large-scale empirical study of slice-based cohesion and coupling metrics possible. Four results from such a study are presented. First, "head-to-head" qualitative and quantitative comparisons of the metrics identify which metrics provide similar views of a program and which provide unique views of a program. This study includes statistical analysis showing that slice-based metrics are not proxies for simple size-based metrics such as lines of code. Second, two longitudinal studies show that slice-based metrics quantify the deterioration of a program as it ages. This serves to validate the metrics: the metrics quantify the degradation that exists during development; turning this around, the metrics can be used to measure the progress of a reengineering effort. Third, baseline values for slice-based metrics are provided. These values act as targets for reengineering efforts with modules having values outside the expected range being the most in need of attention. Finally, slice-based coupling is correlated and compared with slice-based cohesion.