Redesigning of an existing software using design patterns

We describe a case study on redesigning of existing software using design patterns. Although design patterns have spread widely in object-oriented software design, the disordered application of them often makes the design more complicated or worsens performance. In the case study, we introduce a hot-spot based approach to apply design patterns effectively. Then we quantitatively evaluate the effectiveness of applying design patterns to the redesigning. The C&K metrics suite is used for the evaluation. We collect C&K metrics values for two versions of the decision tree learning system. One is a prototype version designed without using design patterns while the other is redesigned using design patterns. We conduct the Mann-Whitny U-test, one of the nonparametric statistics for testing hypotheses about whether two sample values differ. As a result, we find significant differences between the C&K metrics values of the two versions. Finally we discuss the applicability of the C&K metrics to criterion for evaluation of the flexibility and extensibility of software