Using indirect coupling metrics to predict package maintainability and testability

Object-oriented systems are dynamic and have to be constantly maintained, or they become aged and irrelevant. Many costly software issues exist due to poorly designed systems and due to systems which are not easy to test or maintain because of poor designs. Martin's metrics (Martin, 2003) are well-known package design metrics that can be used in early stages of software development. However, since Martin's metrics only measure direct coupling, the authors believe that this limits their accuracy. In previous papers (Almugrin et al., 2014; Almugrin and Melton), we began with Martin's principles and used them to modify his coupling, instability and abstractness metrics based on direct and indirect coupling, respectively. In this paper, we present an experimental study to validate the modified global metrics by showing their relationship to maintainability and testability, and then we construct prediction models for these two external quality attributes. The study results indicate that the new metrics are very promising and lead to improved results.