@conference {Vasilescu:2016:SLM:2884781.2884875,
	title = {The Sky is Not the Limit: Multitasking Across GitHub Projects},
	booktitle = {Proceedings of the 38th International Conference on Software Engineering (ICSE 2016)},
	series = {ICSE {\textquoteright}16},
	year = {2016},
	pages = {994{\textendash}1005},
	publisher = {ACM},
	organization = {ACM},
	address = {New York, NY, USA},
	abstract = {Software development has always inherently required multitasking: developers switch between coding, reviewing, testing, designing, and meeting with colleagues. The advent of software ecosystems like GitHub has enabled something new: the ability to easily switch between projects. Developers also have social incentives to contribute to many projects; prolific contributors gain social recognition and (eventually) economic rewards. Multitasking, however, comes at a cognitive cost: frequent context-switches can lead to distraction, sub-standard work, and even greater stress. In this paper, we gather ecosystem-level data on a group of programmers working on a large collection of projects. We develop models and methods for measuring the rate and breadth of a developers{\textquoteright} context-switching behavior, and we study how context-switching affects their productivity. We also survey developers to understand the reasons for and perceptions of multitasking. We find that the most common reason for multitasking is interrelationships and dependencies between projects. Notably, we find that the rate of switching and breadth (number of projects) of a developer{\textquoteright}s work matter. Developers who work on many projects have higher productivity if they focus on few projects per day. Developers that switch projects too much during the course of a day have lower productivity as they work on more projects overall. Despite these findings, developers perceptions of the benefits of multitasking are varied.
},
	keywords = {github, multitasking, productivity},
	isbn = {978-1-4503-3900-1},
	doi = {10.1145/2884781.2884875},
	url = {http://doi.acm.org/10.1145/2884781.2884875},
	author = {Vasilescu, Bogdan and Blincoe, Kelly and Xuan, Qi and Casalnuovo, Casey and Damian, Daniela and Devanbu, Premkumar and Filkov, Vladimir}
}
@proceedings {1762,
	title = {A Data Set for Social Diversity Studies of GitHub Teams},
	year = {2015},
	month = {05/2015},
	publisher = {IEEE},
	abstract = {Like any other team oriented activity, the software
development process is effected by social diversity in the programmer
teams. The effect of team diversity can be significant,
but also complex, especially in decentralized teams. Discerning
the precise contribution of diversity on teams{\textquoteright} effectiveness
requires quantitative studies of large data sets.
Here we present for the first time a large data set of social
diversity attributes of programmers in GITHUB teams. Using
alias resolution, location data, and gender inference techniques,
we collected a team social diversity data set of 23,493 GITHUB
projects. We illustrate how the data set can be used in practice
with a series of case studies, and we hope its availability will foster
more interest in studying diversity issues in software teams.},
	keywords = {ghtorrent, github},
	url = {http://www.win.tue.nl/~aserebre/cr-msr-data-15.pdf},
	attachments = {https://flosshub.org/sites/flosshub.org/files/cr-msr-data-15.pdf},
	author = {Vasilescu, Bogdan and Serebrenik, Alexander and Filkov, Vladimir}
}
@proceedings {1713,
	title = {Gender and Tenure Diversity in GitHub Teams},
	year = {2015},
	abstract = {Software development is usually a collaborative venture.
Open Source Software (OSS) projects are no exception; indeed,
by design, the OSS approach can accommodate teams
that are more open, geographically distributed, and dynamic
than commercial teams. This, we find, leads to OSS teams
that are quite diverse. Team diversity, predominantly in of-
fline groups, is known to correlate with team output, mostly
with positive effects. How about in OSS?
Using GITHUB, the largest publicly available collection of
OSS projects, we studied how gender and tenure diversity
relate to team productivity and turnover. Using regression
modeling of GITHUB data and the results of a survey, we
show that both gender and tenure diversity are positive and
significant predictors of productivity, together explaining a
sizable fraction of the data variability. These results can
inform decision making on all levels, leading to better outcomes
in recruiting and performance.},
	keywords = {gender, github, team},
	url = {http://bvasiles.github.io/papers/chi15.pdf},
	attachments = {https://flosshub.org/sites/flosshub.org/files/chi15.pdf},
	author = {Vasilescu, Bogdan and Posnett, Daryl and Ray, Baishakhi and van den Brand, Mark G.J. and Serebrenik, Alexander and Devanbu, Premkumar and Filkov, Vladimir}
}
@proceedings {1766,
	title = {Wait For It: Determinants of Pull Request Evaluation Latency on GitHub},
	year = {2015},
	month = {05/2015},
	publisher = {IEEE},
	abstract = {The pull-based development model, enabled by git
and popularised by collaborative coding platforms like BitBucket,
Gitorius, and GitHub, is widely used in distributed software
teams. While this model lowers the barrier to entry for potential
contributors (since anyone can submit pull requests to any repository),
it also increases the burden on integrators (i.e., members
of a project{\textquoteright}s core team, responsible for evaluating the proposed
changes and integrating them into the main development line),
who struggle to keep up with the volume of incoming pull
requests. In this paper we report on a quantitative study that tries
to resolve which factors affect pull request evaluation latency
in GitHub. Using regression modeling on data extracted from
a sample of GitHub projects using the Travis-CI continuous
integration service, we find that latency is a complex issue,
requiring many independent variables to explain adequately.},
	url = {https://bvasiles.github.io/papers/msr15.pdf},
	attachments = {https://flosshub.org/sites/flosshub.org/files/msr15.pdf},
	author = {Yu, Yue and Wang, Huaimin and Filkov, Vladimir and Devanbu, Premkumar and Vasilescu, Bogdan}
}
@proceedings {1685,
	title = {Continuous integration in a social-coding world: Empirical evidence from GitHub},
	year = {2014},
	pages = {5 pages},
	abstract = {Continuous integration is a software engineering practice of frequently merging all developer working copies with a shared main branch, e.g., several times a day.
With the advent of GITHUB, a platform well known for its {\textquotedblleft}social coding{\textquotedblright} features that aid collaboration and sharing, and currently the largest code host in the open source world, collaborative software development has never been more prominent. In GITHUB development one can distinguish between two types of developer contributions to a project: direct ones, coming from a typically small group of developers with write access to the main project repository, and indirect ones, coming from developers who fork the main repository, update their copies locally, and submit pull requests for review and merger.
In this paper we explore how GITHUB developers use continuous integration as well as whether the contribution type (direct versus indirect) and different project characteristics (e.g., main programming language, or project age) are associated with the success of the automatic builds.},
	keywords = {github},
	url = {http://conferences.computer.org/icsme/2014/papers/6146a401.pdf},
	attachments = {https://flosshub.org/sites/flosshub.org/files/ICSME2014ERA.pdf},
	author = {Vasilescu, Bogdan and Serebrenik, Alexander and Schuylenberg, Stef and Wulms, Jules and Brand, Mark G.J.}
}
@conference {Robles:2014:FSD:2597073.2597129,
	title = {FLOSS 2013: A Survey Dataset About Free Software Contributors: Challenges for Curating, Sharing, and Combining},
	booktitle = {Proceedings of the 11th Working Conference on Mining Software Repositories},
	series = {MSR 2014},
	year = {2014},
	pages = {396{\textendash}399},
	publisher = {ACM},
	organization = {ACM},
	address = {New York, NY, USA},
	abstract = {In this data paper we describe a data set obtained by means of performing an on-line survey to over 2,000 Free Libre Open Source Software (FLOSS) contributors. The survey includes questions related to personal characteristics (gender, age, civil status, nationality, etc.), education and level of English, professional status, dedication to FLOSS projects, reasons and motivations, involvement and goals. We describe as well the possibilities and challenges of using private information from the survey when linked with other, publicly available data sources. In this regard, an example of data sharing will be presented and legal, ethical and technical issues will be discussed.
},
	keywords = {anonymization, data combining, data sharing, ethics, free software, microdata, msr data showcase, open data, open source, privacy, Survey},
	isbn = {978-1-4503-2863-0},
	doi = {10.1145/2597073.2597129},
	url = {http://doi.acm.org/10.1145/2597073.2597129},
	attachments = {https://flosshub.org/sites/flosshub.org/files/msr14gregorio.pdf},
	author = {Gregorio Robles and Reina, Laura Arjona and Serebrenik, Alexander and Vasilescu, Bogdan and Gonz{\'a}lez-Barahona, Jes{\'u}s M.}
}
@conference {Vasilescu:2014:SQS:2531602.2531659,
	title = {How Social Q\&A Sites Are Changing Knowledge Sharing in Open Source Software Communities},
	booktitle = {Proceedings of the 17th ACM Conference on Computer Supported Cooperative Work \&\#38; Social Computing},
	series = {CSCW {\textquoteright}14},
	year = {2014},
	pages = {342{\textendash}354},
	publisher = {ACM},
	organization = {ACM},
	address = {New York, NY, USA},
	abstract = {Historically, mailing lists have been the preferred means for coordinating development and user support activities. With the emergence and popularity growth of social Q\&A sites such as the StackExchange network (e.g., StackOverflow), this is beginning to change. Such sites offer different socio-technical incentives to their participants than mailing lists do, e.g., rich web environments to store and manage content collaboratively, or a place to showcase their knowledge and expertise more vividly to peers or potential recruiters. A key difference between StackExchange and mailing lists is gamification, i.e., StackExchange participants compete to obtain reputation points and badges. In this paper, we use a case study of R (a widely-used tool for data analysis) to investigate how mailing list participation has evolved since the launch of StackExchange. Our main contribution is the assembly of a joint data set from the two sources, in which participants in both the texttt{r-help} mailing list and StackExchange are identifiable. This permits their activities to be linked across the two resources and also over time. With this data set we found that user support activities show a strong shift away from texttt{r-help}. In particular, mailing list experts are migrating to StackExchange, where their behaviour is different. First, participants active both on texttt{r-help} and on StackExchange are more active than those who focus exclusively on only one of the two. Second, they provide faster answers on StackExchange than on texttt{r-help}, suggesting they are motivated by the emph{gamified} environment. To our knowledge, our study is the first to directly chart the changes in behaviour of specific contributors as they migrate into gamified environments, and has important implications for knowledge management in software engineering.},
	keywords = {a, crowdsourced knowledge, gamification., mailing lists, open source, social q\&\#38},
	isbn = {978-1-4503-2540-0},
	doi = {10.1145/2531602.2531659},
	url = {http://doi.acm.org/10.1145/2531602.2531659},
	attachments = {https://flosshub.org/sites/flosshub.org/files/cscw14.pdf},
	author = {Vasilescu, Bogdan and Serebrenik, Alexander and Devanbu, Prem and Filkov, Vladimir}
}
@conference {Gousios:2014:LGG:2597073.2597126,
	title = {Lean GHTorrent: GitHub Data on Demand},
	booktitle = {Proceedings of the 11th Working Conference on Mining Software Repositories},
	series = {MSR 2014},
	year = {2014},
	pages = {384{\textendash}387},
	publisher = {ACM},
	organization = {ACM},
	address = {New York, NY, USA},
	abstract = {In recent years, GitHub has become the largest code host in the world, with more than 5M developers collaborating across 10M repositories. Numerous popular open source projects (such as Ruby on Rails, Homebrew, Bootstrap, Django or jQuery) have chosen GitHub as their host and have migrated their code base to it. GitHub offers a tremendous research potential. For instance, it is a flagship for current open source development, a place for developers to showcase their expertise to peers or potential recruiters, and the platform where social coding features or pull requests emerged. However, GitHub data is, to date, largely underexplored. To facilitate studies of GitHub, we have created GHTorrent, a scalable, queriable, offline mirror of the data offered through the GitHub REST API. In this paper we present a novel feature of GHTorrent designed to offer customisable data dumps on demand. The new GHTorrent data-on-demand service offers users the possibility to request via a web form up-to-date GHTorrent data dumps for any collection of GitHub repositories. We hope that by offering customisable GHTorrent data dumps we will not only lower the "barrier for entry" even further for researchers interested in mining GitHub data (thus encourage researchers to intensify their mining efforts), but also enhance the replicability of GitHub studies (since a snapshot of the data on which the results were obtained can now easily accompany each study).
},
	keywords = {data on demand, dataset, github, msr data showcase},
	isbn = {978-1-4503-2863-0},
	doi = {10.1145/2597073.2597126},
	url = {http://doi.acm.org/10.1145/2597073.2597126},
	attachments = {https://flosshub.org/sites/flosshub.org/files/lean-ghtorrent_0.pdf},
	author = {Gousios, Georgios and Vasilescu, Bogdan and Serebrenik, Alexander and Zaidman, Andy}
}
@conference {Pletea:2014:SES:2597073.2597117,
	title = {Security and Emotion: Sentiment Analysis of Security Discussions on GitHub},
	booktitle = {Proceedings of the 11th Working Conference on Mining Software Repositories},
	series = {MSR 2014},
	year = {2014},
	pages = {348{\textendash}351},
	publisher = {ACM},
	organization = {ACM},
	address = {New York, NY, USA},
	abstract = {Application security is becoming increasingly prevalent during software and especially web application development. Consequently, countermeasures are continuously being discussed and built into applications, with the goal of reducing the risk that unauthorized code will be able to access, steal, modify, or delete sensitive data. In this paper we gauged the presence and atmosphere surrounding security-related discussions on GitHub, as mined from discussions around commits and pull requests. First, we found that security related discussions account for approximately 10\% of all discussions on GitHub. Second, we found that more negative emotions are expressed in security-related discussions than in other discussions. These findings confirm the importance of properly training developers to address security concerns in their applications as well as the need to test applications thoroughly for security vulnerabilities in order to reduce frustration and improve overall project atmosphere.
},
	keywords = {github, mining challenge, msr challenge, security, sentiment analysis},
	isbn = {978-1-4503-2863-0},
	doi = {10.1145/2597073.2597117},
	url = {http://doi.acm.org/10.1145/2597073.2597117},
	attachments = {https://flosshub.org/sites/flosshub.org/files/pletea.pdf},
	author = {Pletea, Daniel and Vasilescu, Bogdan and Serebrenik, Alexander}
}
@mastersthesis {1718,
	title = {Social aspects of collaboration in online software communities},
	year = {2014},
	abstract = {Software engineering is inherently a collaborative venture, involving many stakeholders that coordinate their efforts to produce large software systems. In distributed (online) settings, endemic to open-source software (OSS) development, such collaborations span geographies and cultures. Contributors with different skill sets, personalities, cultural backgrounds, or geographic locations self-organise in online software communities and voluntarily contribute to a collaborative effort, such as developing and evolving software systems, offering user support, or sharing knowledge. Myriads of online software communities exist. Among the most visible are those around the Linux operating system and its various distributions, the Gnome desktop environment, the Apache or Mozilla software foundations or, more recently, the GitHub repository hosting platform, or the Stack Exchange network of question and answer sites (e.g., Stack Overflow for programming-related questions).

Different communities operate by different rules and offer different incentives to contribute. More traditional communities such as Gnome or Apache rely mostly on the intrinsic motivations of developers. In contrast, younger communities offer social media and gamification features (e.g., contributors to Stack Overflow are rewarded for their activity with reputation points and badges) as well as increased visibility to peers (e.g., the activity and achievements of GitHub and Stack Overflow contributors are aggregated and displayed on public profile pages). Furthermore, online software communities are often interdependent. For example, a Gnome contributor may engage simultaneously in different communities part of the Gnome ecosystem, where she may take on different roles or instead choose to specialise in similar tasks. Similarly, a GitHub contributor may participate simultaneously in Stack Overflow, where she may seek help from peers or instead share her knowledge and expertise to help educate others.

Starting from the recent realisation of the empirical software engineering research community that social aspects are at least as important for the success of distributed collaborations as technical ones, this dissertation is an attempt to understand collaboration in representative online software communities from a social perspective. To this end, we mines and analyses a wealth of publicly available trace data using state-of-the-art statistical techniques, from various standpoints outlined below. The work in this dissertation sits at the intersection of two research communities, computer-supported cooperative work (CSCW) and software engineering (SE). Consequently, it offers contributions to both SE and CSCW, ranging from methods and tools to mine and analyse large amounts of (social) trace data, to practical implications for software maintainability, software team management, knowledge management or community design.

First, we propose individual-level measures of workload, involvement, and specialisation of labour in online software development communities, and report on a case study of the Gnome ecosystem community. Additionally, we propose a community-level measure of skill diversity with respect to a certain technical skill, such as knowledge of a given programming language. Social interactions between contributors to software development communities and their degree of participation have been reported repeatedly to influence software quality and complexity. Similarly, skill heterogeneity in a software community is important for the community{\textquoteright}s survival and performance.

Second, we analyse the effects of simultaneously contributing to multiple communities on individual working rhythms. We focus on developers contributing source code to GitHub repositories while seeking and sharing knowledge on Stack Overflow. Despite the popularity of Stack Overflow, its role in the work cycle of OSS developers is yet to be understood. On the one hand, participation in it has the potential to increase the knowledge of individual developers thus improving and speeding up the development process. On the other hand, participation in Stack Overflow may interrupt the regular working rhythm of a developer, hence also possibly slow down the development process. We show that active GitHub contributors typically engage in Stack Overflow as experts, asking few questions and providing many answers for others. Moreover, despite the interruptions incurred, the Stack Overflow activity rate correlates with the code changing rate on GitHub.

Third, we chart the changes in behaviour of contributors to online knowledge sharing communities as they migrate into gamified environments. To this end, we assemble a joint data set for R (a widely-used tool for data analysis) by integrating data from mailing lists and Stack Exchange sites, having activities of individual contributors linked across the two resources and also over time. We find that user support activities show a strong shift away from mailing lists (historically the hub for development and user support activities in online software communities) and towards Stack Exchange. Moreover, knowledge providers contributing to both communities provide faster answers on Stack Exchange than on the mailing list, and their total output increases after the transition.

Fourth, we revisit the gamified Stack Overflow environment from the perspectives of gender representation and participation patterns, in comparison to traditional information sharing venues such as mailing lists. In addition to encouraging competitiveness through its gamification features, anecdotal evidence around Stack Overflow suggests that it is an unfriendly community that promotes one-upmanship, or fosters flame-wars and the down-voting of individuals. We find that while women are under-represented in all studied communities, they show different participation patterns on Stack Overflow, where they disengage sooner than men. However, relative to the duration of their engagement in the community, women on Stack Overflow are at least as active as men.

Fifth, we address the recurring mining software repositories challenge of inconsistent identity data. To this end, we analyse the robustness of two representative existing identity merging algorithms with respect to different types of noise typical of software repositories, and we propose a new identity merging algorithm inspired by Latent Semantic Analysis, a popular information retrieval technique expected to perform well in presence of noise. Using data extracted from Gnome Git repositories, we evaluate the performance of our algorithm empirically by means of cross-validation, and show an improvement over existing approaches in terms of precision and recall on worst-case input data.

Last, we provide an example of the applicability of methods developed or refined as part of this work beyond online software communities. Specifically, we propose a metrics suite to study the health of software engineering conferences and conference communities, measuring such attributes as stability, openness to new authors, or introversion. Using this metrics suite, we assess the health of 11 established software engineering conferences over a period of more than 10 years. In general, we find that software engineering conferences are healthy, with some notable differences depending on the chosen health metric, or a conference{\textquoteright}s wide or narrow scope. Beyond demonstrating the generalisability of our techniques, this latter study has implications for conference steering committees or program committee chairs wishing to assess their selection process, or prospective authors trying to decide in which conferences to publish.},
	url = {http://www.win.tue.nl/ipa/?event=social-aspects-of-collaboration-in-online-software-communities},
	author = {Vasilescu, Bogdan}
}
@conference {Vasilescu:2014:SDH:2556420.2556833,
	title = {Software Developers Are Humans, Too!},
	booktitle = {Proceedings of the Companion Publication of the 17th ACM Conference on Computer Supported Cooperative Work \&\#38; Social Computing},
	series = {CSCW Companion {\textquoteright}14},
	year = {2014},
	pages = {97{\textendash}100},
	publisher = {ACM},
	organization = {ACM},
	address = {New York, NY, USA},
	abstract = {Open-source communities can be seen as knowledge-sharing ecosystems: participants learn from the community and from one another, and share their knowledge through contributions to the source code repositories or by offering support to users. With the emergence and growing popularity of social media sites targeting software developers (e.g., StackOverflow, GitHub), the paths through which knowledge flows within open-source software knowledge-sharing ecosystems are also beginning to change. My dissertation research seeks to raise our understanding of these changes.},
	keywords = {human aspects, open-source, software developers},
	isbn = {978-1-4503-2541-7},
	doi = {10.1145/2556420.2556833},
	url = {http://doi.acm.org/10.1145/2556420.2556833},
	author = {Vasilescu, Bogdan}
}
@inbook {1630,
	title = {The Babel of Software Development: Linguistic Diversity in Open Source},
	booktitle = {Social Informatics},
	series = {Lecture Notes in Computer Science},
	volume = {8238},
	year = {2013},
	pages = {391-404},
	publisher = {Springer International Publishing},
	organization = {Springer International Publishing},
	isbn = {978-3-319-03259-7},
	doi = {10.1007/978-3-319-03260-3_34},
	url = {http://dx.doi.org/10.1007/978-3-319-03260-3_34},
	attachments = {https://flosshub.org/sites/flosshub.org/files/socinfo13.pdf},
	author = {Vasilescu, Bogdan and Serebrenik, Alexander and Brand, MarkG.J.},
	editor = {Jatowt, Adam and Lim, Ee-Peng and Ding, Ying and Miura, Asako and Tezuka, Taro and Dias, Ga{\"e}l and Tanaka, Katsumi and Flanagin, Andrew and Dai, BingTian}
}
