Design Properties and Object-Oriented Software Changeability

The assessment of the changeability of software systems is of major concern for buyers of the large systems found in fast-moving domains such as telecommunications. One way of approaching this problem is to investigate the dependency between the changeability of the software and its design, with the goal of finding design properties that can be used as changeability indicators. In our research, we defined a model of software changes and change impacts and implemented it for the C++ language. Furthermore, we identified a set of nine object-oriented (OO) design metrics, four of which are specifically geared towards changeability detection. The model and the metrics were applied to three test systems of industrial size. The experiment showed a high correlation, across systems and across changes, between changeability and the access to a class by other classes through method invocation or variable access. On the other hand, no result could support the hypothesis that the depth of the inheritance tree has some influence on changeability. Furthermore, our results confirm the observation of others that the use of inheritance is rather limited in industrial systems.