@conference {926,
	title = {Tracking concept drift of software projects using defect prediction quality},
	booktitle = {2009 6th IEEE International Working Conference on Mining Software Repositories (MSR)2009 6th IEEE International Working Conference on Mining Software Repositories},
	year = {2009},
	pages = {51 - 60},
	publisher = {IEEE},
	organization = {IEEE},
	address = {Vancouver, BC, Canada},
	abstract = {Defect prediction is an important task in the mining of software repositories, but the quality of predictions varies strongly within and across software projects. In this paper we investigate the reasons why the prediction quality is so fluctuating due to the altering nature of the bug (or defect) fixing process. Therefore, we adopt the notion of a concept drift, which denotes that the defect prediction model has become unsuitable as set of influencing features has changed - usually due to a change in the underlying bug generation process (i.e., the concept). We explore four open source projects (Eclipse, OpenOffice, Netbeans and Mozilla) and construct file-level and project-level features for each of them from their respective CVS and Bugzilla repositories. We then use this data to build defect prediction models and visualize the prediction quality along the time axis. These visualizations allow us to identify concept drifts and - as a consequence - phases of stability and instability expressed in the level of defect prediction quality. Further, we identify those project features, which are influencing the defect prediction quality using both a tree induction-algorithm and a linear regression model. Our experiments uncover that software systems are subject to considerable concept drifts in their evolution history. Specifically, we observe that the change in number of authors editing a file and the number of defects fixed by them contribute to a project{\textquoteright}s concept drift and therefore influence the defect prediction quality. Our findings suggest that project managers using defect prediction models for decision making should be aware of the actual phase of stability or instability due to a potential concept drift.},
	keywords = {bugzilla, cvs, defect prediction, eclipse, mozilla, netbeans, openoffice},
	isbn = {978-1-4244-3493-0},
	doi = {10.1109/MSR.2009.5069480},
	attachments = {https://flosshub.org/sites/flosshub.org/files/51MSR2009_0111_Ekanayake_Jayalath.pdf},
	author = {Ekanayake, Jayalath and Tappolet, Jonas and Gall, Harald C. and Bernstein, Abraham}
}
@conference {973,
	title = {On the relation of refactorings and software defect prediction},
	booktitle = {Proceedings of the 2008 international workshop on Mining software repositories  - MSR {\textquoteright}08},
	year = {2008},
	month = {05/2008},
	pages = {35-38},
	publisher = {ACM Press},
	organization = {ACM Press},
	address = {New York, New York, USA},
	abstract = {This paper analyzes the influence of evolution activities such as refactoring on software defects. In a case study of five open source projects we used attributes of software evolution to predict defects in time periods of six months. We use versioning and issue tracking systems to extract 110 data mining features, which are separated into refactoring and non-refactoring related features. These features are used as input into classification algorithms that create prediction models for software defects. We found out that refactoring related features as well as non-refactoring related features lead to high quality prediction models. Additionally, we discovered that refactorings and defects have an inverse correlation: The number of software defects decreases, if the number of refactorings increased in the preceding time period. As a result, refactoring should be a significant part of both bug fixes and other evolutionary changes to reduce software defects.},
	keywords = {argouml, bug fixing, bug reports, defects, evolution, jboss, liferay, prediction, refactoring, spring, weka, xdoclet},
	isbn = {9781605580241},
	doi = {10.1145/1370750.1370759},
	attachments = {https://flosshub.org/sites/flosshub.org/files/p35-ratzinger.pdf},
	author = {Sigmund, Thomas and Gall, Harald C. and Ratzinger, Jacek}
}
