A Case Study of Defect-Density and Change-Density and their Progress over Time

We have performed an empirical case study, investigating defect-density and change-density of a reusable framework compared with one application reusing it over time at a large Oil and Gas company in Norway, Statoil ASA. The framework, called JEF, consists of seven components grouped together, and the application, called DCF, reuses the framework, without modifications to the framework. We analyzed all trouble reports and change requests from three releases of both. Change requests in our study covered any changes (not correcting defects) in the requirements, while trouble reports covered any reported defects. Additionally, we have investigated the relation between defect-density and change-density both for the reusable JEF framework and the application. The results revealed that the defectdensity of the reusable framework was lower than the application. The JEF framework had higher changedensity in the first release, but lower change-density than the DCF application over the successive releases. For the DCF application, on the other hand, a slow increase in change-density appeared. On the relation between change-density and defect-density for the JEF framework, we found a decreasing defect-density and change-density. The DCF application here showed a decreasing defect-density, with an increasing changedensity. The results show that the quality of the reusable framework improves and it becomes more stable over several releases, which is important for reliability of the framework and assigning resources.