Inheritance Tree Shapes and Reuse

The shapes of forests of inheritance trees can affect the amount of code reuse in an object-oriented system. Designers can benefit from knowing how structuring decisions affect reuse, so that they can make more optimal decisions. We show that a set of objective measures can classify forests of inheritance trees into a set of five shape classes. These shape classes determine bounds on reuse measures based on the notion of code savings. The reuse measures impart an ordering on the shape classes that demonstrates that some shapes have more capacity to support reuse through inheritance. An initial empirical study shows that the application of the measures and demonstrates that real inheritance forests can be objectively and automatically classified into one of the five shape classes. Index terms — software measurement and metrics, object-oriented software, inheritance, software reuse.