Predicting fault-prone modules with case-based reasoning

Software quality classification models seek to predict quality factors such as whether a module will be fault prone, or not. Case based reasoning (CBR) is a modeling technique that seeks to answer new questions by identifying similar "cases" from the past. When applied to software reliability, the working hypothesis of our approach is this: a module currently under development is probably fault prone if a module with similar product and process attributes in an earlier release was fault prone. The contribution of the paper is application of case based reasoning to software quality modeling. To the best of our knowledge, this is the first time that case based reasoning has been used to identify fault prone modules. A case study illustrates our approach and provides evidence that case based reasoning can be the basis for useful software quality classification models that are competitive with discriminant models. The case study revisits data from a previously published nonparametric discriminant analysis study. The Type II misclassification rate of the CBR model was substantially better than that of the discriminant model. Although the Type I misclassification rate was slightly greater and the overall misclassification rate was only slightly less, the CBR model was preferred when costs of misclassification were considered.