Code Ownership: Impact on Maintainability

Software systems erode during development, which results in high maintenance costs in the long term. Is it possible to narrow down where exactly this erosion happens? Can we infer the future erosion based on past code changes? In this paper we investigate code ownership and show that a further step of code quality decrease is more likely to happen due to the changes in source files modified by several developers in the past, compared to files with clear ownership. We estimate the level of code ownership and maintainability changes for every commit of three open-source and one proprietary software systems. With the help of Wilcoxon rank test we compare the ownership values of the files in commits resulting maintainability increase with those of decreasing the maintainability. Three tests out of the four gave strong results and the fourth one did not contradict them either. The conclusion of this study is a generalization of the already known fact that common code is more error-prone than those of developed by fewer developers. This result could be utilized in identifying the “hot spots” of the source code from maintainability point of view. A possible IDE plug-in, which indicates the risk of decreasing the maintainability of the source code, could help the architect and warn the developers.