@conference {KHF16,
	title = {A Code Refactoring Dataset and Its Assessment Regarding Software Maintainability},
	booktitle = {Proceedings of the 23rd IEEE International Conference on Software Analysis, Evolution, and Reengineering (SANER 2016)},
	year = {2016},
	pages = {599{\textendash}603},
	publisher = {IEEE Computer Society},
	organization = {IEEE Computer Society},
	address = {Suita, Osaka, Japan},
	abstract = {It is very common in various fields that there is a gap between theoretical results and their practical applications. This is true for code refactoring as well, which has a solid theoretical background while being used in development practice at the same time. However, more and more studies suggest that developers perform code refactoring entirely differently than the theory would suggest. Our paper encourages the further investigation of code refactorings in practice by providing an excessive open dataset of source code metrics and applied refactorings through several releases of 7 open-source systems. As a first step of processing this dataset, we examined the quality attributes of the refactored source code classes and the values of source code metrics improved by those refactorings. Our early results show that lower maintainability indeed triggers more code refactorings in practice and these refactorings significantly decrease complexity, code lines, coupling and clone metrics. However, we observed a decrease in comment related metrics in the refactored code.},
	keywords = {Code refactoring, Empirical study, Software maintainability},
	doi = {10.1109/SANER.2016.42},
	url = {http://ieeexplore.ieee.org/document/7476680/},
	author = {K{\'a}d{\'a}r, Istv{\'a}n and P Heged{\H u}s and Rudolf Ferenc and Tibor Gyim{\'o}thy}
}
@conference {FHF15,
	title = {Code Ownership: Impact on Maintainability},
	booktitle = {Proceedings of the 15th International Conference on Computational Science and Its Applications (ICCSA 2015)},
	series = {Lecture Notes in Computer Science (LNCS)},
	volume = {9159},
	year = {2015},
	month = {jun},
	pages = {3{\textendash}19},
	publisher = {Springer-Verlag},
	organization = {Springer-Verlag},
	address = {Banff, Alberta, Canada},
	abstract = {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 {\textquotedblleft}hot spots{\textquotedblright} 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.},
	keywords = {Code ownership, ISO/IEC 25010, Source code maintainability, Wilcoxon test},
	doi = {10.1007/978-3-319-21413-9_1},
	url = {https://link.springer.com/chapter/10.1007\%2F978-3-319-21413-9_1},
	author = {Farag{\'o}, Csaba and P Heged{\H u}s and Rudolf Ferenc}
}
@conference {FHF15b,
	title = {Cumulative Code Churn: Impact on Maintainability},
	booktitle = {Proceedings of the 15th IEEE International Working Conference on Source Code Analysis and Manipulation (SCAM 2015)},
	year = {2015},
	month = {sep},
	pages = {141{\textendash}150},
	publisher = {IEEE Computer Society},
	organization = {IEEE Computer Society},
	address = {Bremen, Germany},
	abstract = {It is a well-known phenomena that the source code of software systems erodes during development, which results in higher maintenance costs in the long term. But can we somehow narrow down where exactly this erosion happens? Is it possible to infer the future erosion based on past code changes? Do modifications performed on frequently changing code have worse effect on software maintainability than those affecting less frequently modified code? In this study we investigated these questions and the results indicate that code churn indeed increases the pace of code erosion. We calculated cumulative code churn values and maintainability changes for every version control commit operation of three open-source and one proprietary software system. With the help of Wilcoxon rank test we compared the cumulative code churn values of the files in commits resulting maintainability increase with those of decreasing the maintainability. In the case of three systems the test showed very strong significance and in one case it resulted in strong significance (p-values 0.00235, 0.00436, 0.00018 and 0.03616). These results support our preliminary assumption that modifying high-churn code is more likely to decrease the overall maintainability of a software system, which can be thought of as the generalization of the already known phenomena that code churn results in higher number of defects.},
	keywords = {code churn, ISO/IEC 25010, Source code maintainability, Wilcoxon test},
	doi = {10.1109/SCAM.2015.7335410},
	url = {http://ieeexplore.ieee.org/document/7335410/},
	author = {Farag{\'o}, Csaba and P Heged{\H u}s and Rudolf Ferenc}
}
@article {FHV14,
	title = {Connection Between Version Control Operations and Quality Change of the Source Code},
	journal = {Acta Cybernetica},
	volume = {21},
	number = {4},
	year = {2014},
	pages = {585{\textendash}607},
	abstract = {Software erosion is a well-known phenomena, meaning that software quality is continuously decreasing due to the ever-ongoing modifications in the source code. In this research work we investigated this phenomena by studying the impact of version control commit operations (add, update, delete) on the quality of the code. We calculated the ISO/IEC 9126 quality attributes for thousands of revisions of an industrial and three open-source software systems with the help of the Columbus Quality Model. We also collected the cardinality of each version control operation type for every investigated revision. We performed Chisquared tests on contingency tables with rows of quality change and columns of version control operation commit types. We compared the results with random data as well. We identified that the relationship between the version control operations and quality change is quite strong. Great maintainability improvements are mostly caused by commits containing Add operation. Commits containing file updates only tend to have a negative impact on the quality. Deletions have a weak connection with quality, and we could not formulate a general statement.},
	keywords = {Case Study, ISO/IEC 9126, Software Erosion, Software maintainability, Source Code Version Control},
	issn = {0324-721X},
	url = {http://publicatio.bibl.u-szeged.hu/8394/},
	author = {Farag{\'o}, Csaba and P Heged{\H u}s and V{\'e}gh, {\'A}d{\'a}m Zolt{\'a}n and Rudolf Ferenc}
}
@conference {LHF14,
	title = {The Connection of the Bug Density and Maintainability of Classes},
	booktitle = {8th International Workshop on Software Quality and Maintainability},
	series = {SQM},
	year = {2014},
	note = {Presentation only},
	month = {feb},
	address = {Antwerp, Belgium},
	abstract = {Measuring software product maintainability is a central issue in software engineering which led to a number of different practical quality models. Besides system level assessments it is also desirable that these models provide technical quality information at source code element level (e.g. classes, methods) to aid the improvement of the software. Although many existing models give an ordered list of source code elements that should be improved, it is unclear how these improvements affect other important quality indicators of the system, e.g. bug density. In this paper we empirically investigate the connection of bug numbers in the classes of different open-source systems and the class level maintainability measures of our ColumbusQM probabilistic quality model using open-access bug datasets. We show that classes with lower maintainability score contain significantly more bugs than more maintainable classes. Moreover, in terms of correctness and completeness, ColumbusQM competes with statistical and machine learning prediction models especially trained on the bug data using product metrics as predictors. This is a great achievement in the light of that our model needs no training and its purpose is different (e.g. to estimate testability, or development costs) than those of the bug prediction models. In summary, we show that improving the maintainability of a software according to the suggestions of our quality model will expectedly also reduce its bug density.},
	keywords = {Bug density, Bug prediction, Class level maintainability, ColumbusQM, ISO/IEC 25010, Software maintainability},
	author = {Lad{\'a}nyi, Gergely and P Heged{\H u}s and Rudolf Ferenc and Istv{\'a}n Siket and Tibor Gyim{\'o}thy}
}
@conference {16329,
	title = {A Cost Model Based on Software Maintainability},
	booktitle = {Proceedings of the 28th IEEE International Conference on Software Maintenance (ICSM)},
	year = {2012},
	pages = {316{\textendash}325},
	publisher = {IEEE Comput. Soc. Press},
	organization = {IEEE Comput. Soc. Press},
	address = {Los Alamitos},
	author = {Tibor Bakota and P Heged{\H u}s and G. Lad{\'a}nyi and K{\"o}rtv{\'e}lyesi, P and Rudolf Ferenc and Tibor Gyim{\'o}thy},
	editor = {Paolo Tonella and Massimiliano Di Penta and Jonathan I Maletic}
}
@conference {THJ10,
	title = {Comparison of Different Impact Analysis Methods and Programmer{\textquoteright}s Opinion {\textendash} an Empirical Study},
	booktitle = {Proceedings of the 8th International Conference on the Principles and Practice of Programming in Java (PPPJ{\textquoteright}10)},
	year = {2010},
	pages = {109-118},
	publisher = {ACM},
	organization = {ACM},
	author = {T{\'o}th, G. and P Heged{\H u}s and Judit J{\'a}sz and {\'A}rp{\'a}d Besz{\'e}des and Tibor Gyim{\'o}thy}
}
@booklet {KBH09,
	title = {A common exchange format for design pattern detection tools},
	year = {2009},
	note = {IAI-TR-2009-03},
	author = {G. Kniesel and A. Binun and P Heged{\H u}s and F{\"u}l{\"o}p, L.J. and A. Chatzigeorgiou and Y.-G. Gueheneuc and N. Tsantalis}
}
@conference {FIVHF08,
	title = {Comparing and Evaluating Design Pattern Miner Tools},
	booktitle = {Annales Universitatis Scientiarum Budapestinensis de Rolando Eotvos Nominatae Sectio Computarotica},
	volume = {31},
	year = {2009},
	pages = {167-184},
	publisher = {Department of Computer Algebra, E{\"o}tv{\"o}s Lor{\'a}nd University},
	organization = {Department of Computer Algebra, E{\"o}tv{\"o}s Lor{\'a}nd University},
	author = {F{\"u}l{\"o}p, L.J. and {\'A}. Ilia and {\'A}. Z. V{\'e}gh and P Heged{\H u}s and Rudolf Ferenc}
}
