Stack Overflow is the largest Q&A website for developers, providing a huge amount of copyable code snippets. Using these snippets raises various maintenance and legal issues. The Stack Overflow license requires attribution, i.e., referencing the original question or answer, and requires derived work to adopt the license. While there is a heated debate on Stack Overflow's license model for code snippets and the required attribution, little is known about the extent to which snippets are copied from Stack Overflow without proper attribution. In this paper, we present the results of an empirical study which analyzes attributed usages of Stack Overflow code snippets in GitHub projects for the most common programming languages, and estimates a lower bound for unattributed usages in Java files. On average, one out of 32 repositories contained a reference to Stack Overflow. Further, we found that developers rather refer to the whole thread on Stack Overflow than to a specific answer. For Java, at least two thirds of the copied snippets are not attributed.

Background: Performance bugs can lead to severe issues regarding computation efficiency, power consumption, and user experience. Locating these bugs is a difficult task because developers have to judge for every costly operation whether runtime is consumed necessarily or unnecessarily. Objective: We wanted to investigate how developers, when locating performance bugs, navigate through the code, understand the program, and communicate the detected issues. Method: We performed a qualitative user study observing twelve developers trying to fix documented performance bugs in two open source projects. The developers worked with a profiling and analysis tool that visually depicts runtime information in a list representation and embedded into the source code view. Results: We identified typical navigation strategies developers used for pinpointing the bug, for instance, following method calls based on runtime consumption. The integration of visualization and code helped developers to understand the bug. Sketches visualizing data structures and algorithms turned out to be valuable for externalizing and communicating the comprehension process for complex bugs. Conclusion: Fixing a performance bug is a code comprehension and navigation problem. Flexible navigation features based on executed methods and a close integration of source code and performance information support the process.

Sketches and diagrams play an important role in the daily work of software developers. In this paper, we investigate the use of sketches and diagrams in software engineering practice. To this end, we used both quantitative and qual- itative methods. We present the results of an exploratory study in three companies and an online survey with 394 participants. Our participants included software develop- ers, software architects, project managers, consultants, as well as researchers. They worked in different countries and on projects from a wide range of application areas. Most questions in the survey were related to the last sketch or dia- gram that the participants had created. Contrary to our ex- pectations and previous work, the majority of sketches and diagrams contained at least some UML elements. However, most of them were informal. The most common purposes for creating sketches and diagrams were designing, explain- ing, and understanding, but analyzing requirements was also named often. More than half of the sketches and diagrams were created on analog media like paper or whiteboards and have been revised after creation. Most of them were used for more than a week and were archived. We found that the majority of participants related their sketches to methods, classes, or packages, but not to source code artifacts with a lower level of abstraction.

So far, research on model merging has mostly focused on algorithmic problems. But, there are various situations when software engineers have to compare and merge different models manually or at least make important decisions. In this paper, we provide insights into the process of how users compare and merge visual models. To this end, we observed people’s activities when manually merging UML class diagrams and analyzed the recorded data following the Grounded Theory approach. To illustrate the usefulness of our results we derived some guidelines for tool design.

In source code files, fields and methods are arranged in linear order. Modern programming languages such as Java do not constrain this order—developers are free to choose any sequence. In this paper we examine the largely unexplored strategies developers apply for ordering fields and methods: First, we use visualization to explore different ordering criteria within two open source Java projects. Second, we verify our observations in a metric-based analysis on an extended set of 16 projects. Third, we present the results of a survey that reflects the opinion and applied ordering strategies of 52 developers. 87% of the participants agreed that ordering of fields and methods is meaningful or important. Our results suggest that there exists a set of criteria repeatedly used for ordering. Among these, the categories defined in the official Java Code Conventions appear to be the primary ordering criterion. However, in the individual strategies of the participants of the survey, we identified 15 ordering criteria additional to the five criteria we considered in the empirical analysis.

Radial visualizations play an important role in the information visualization community. But the decision to choose a radial coordinate system is rather based on intuition than on scientific foundations. The empirical approach presented in this paper aims at uncovering strengths and weaknesses of radial visualizations by comparing them to equivalent ones in Cartesian coordinate systems. We identified memorizing positions of visual elements as a generic task when working with visualizations. A first study with 674 participants provides a broad data spectrum for exploring differences between the two visualization types. A second, complementing study with fewer participants focuses on further questions raised by the first study. Our findings document that Cartesian visualizations tend to outperform their radial counterparts especially with respect to answer times. Nonetheless, radial visualization seem to be more appropriate for focusing on a particular data dimension.

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Neuigkeiten und Aktuelles

Neuigkeiten und Aktuelles


Am Lehrstuhl für Datenbanken und Informationssysteme der Universität Trier ist zum

1. Oktober 2017 eine Stelle als

wissenschaftliche Mitarbeiterin/wissenschaftlicher Mitarbeiter

(100%, TV-L 13)

zu besetzen. Die Stelle ist zunächstauf drei Jahre befristet.


Die Möglichkeit zur Promotion wird gegeben.


Rückfragen beantwortet Ihnen gerne Prof. Ralf Schenkel unter der Mailadresse oder unter 0651/201-2040.





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Ihr Weg zu uns

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