Physical separation with class refinements and method refinements à la AHEAD and virtual separation using annotations à la #ifdef or CIDE are two competing implementation approaches for software product lines with complementary advantages. Although both approaches have been mainly discussed in isolation, we strive for an integration to leverage the respective advantages. In this paper, we lay the foundation for such an integration by providing a model that supports both physical and virtual separation and by describing refactorings in both directions. We prove the refactorings complete, so every virtually separated product line can be automatically transformed into a physically separated one (replacing annotations by refinements) and vice versa. To demonstrate the feasibility of our approach, we have implemented the refactorings in our tool CIDE and conducted four case studies.

The C preprocessor ( CPP ) is a simple and language-independent tool, widely used to implement variable software systems using conditional compilation (i.e., by including or excluding annotated code). Although CPP provides powerful means to express variability, it has been criticized for allowing arbitrary annotations that break the underlying structure of the source code. We distinguish between disciplined annotations, which align with the structure of the source code, and undisciplined annotations, which do not. Several studies suggest that especially the latter type of annotations makes it hard to (automatically) analyze the code. However, little is known about whether the type of annotations has an effect on program comprehension. We address this issue by means of a controlled experiment with human subjects. We designed similar tasks for both, disciplined and undisciplined annotations, to measure program comprehension. Then, we measured the performance of the subjects regarding correctness and response time for solving the tasks. Our results suggest that there are no differences between disciplined and undisciplined annotations from a program-comprehension perspective. Nevertheless, we observed that finding and correcting errors is a time-consuming and tedious task in the presence of preprocessor annotations.

Some limitations of object-oriented mechanisms are known to cause code clones (e.g., extension using inheritance). Novel programming paradigms such as feature-oriented programming (FOP) aim at alleviating these limitations. However, it is an open issue whether FOP is really able to avoid code clones or whether it even facilitates (FOP-related) clones. To address this issue, we conduct an empirical analysis on ten feature-oriented software product lines with respect to code cloning. We found that there is a considerable amount of clones in feature-oriented software product lines and that a large fraction of these clones is FOP-related (i.e., caused by limitations of feature-oriented mechanisms). Based on our results, we initiate a discussion on the reasons for FOP-related clones and on how to cope with them. We exemplary show how such clones can be removed by the application of refactoring.

Many open-source software projects depend on a few core developers, who take over both the bulk of coordination and programming tasks. They are supported by peripheral developers, who contribute either via discussions or programming tasks, often for a limited time. It is unclear what role these peripheral developers play in the programming and communication efforts, as well as the temporary task-related sub-groups in the projects. We mine code-repository data and mailing-list discussions to model the relationships and contributions of developers in a social network and devise a method to analyze the temporal collaboration structures in communication and programming, learning about the strength and stability of social sub-groups in open-source software projects. Our method uses multi-modal social networks on a series of time windows. Previous work has reduced the network structure representing developer collaboration to networks with only one type of interaction, which impedes the simultaneous analysis of more than one type of interaction. We use both communication and version-control data of open-source software projects and model different types of interaction over time. To demonstrate the practicability of our measurement and analysis method, we investigate 10 substantial and popular open-source software projects and show that, if sub-groups evolve, modeling these sub-groups helps predict the future evolution of interaction levels of programmers and groups of developers. Our method allows maintainers and other stakeholders of open-source software projects to assess instabilities and organizational changes in developer interaction and can be applied to different use cases in organizational analysis, such as understanding the dynamics of a specific incident or discussion.

Software product lines (SPLs) and adaptive systems aim at variability to cope with changing requirements. Variability can be described in terms of features , which are central for development and configuration of SPLs. In traditional SPLs, features are bound statically before runtime. By contrast, adaptive systems support feature binding at runtime and are sometimes called dynamic SPLs (DSPLs) . DSPLs are usually built from coarse-grained components, which reduces the number of possible application scenarios. To overcome this limitation, we closely integrate static binding of traditional SPLs and runtime adaptation of DSPLs. We achieve this integration by statically generating a tailor-made DSPL from a highly customizable SPL. The generated DSPL provides only the runtime variability required by a particular application scenario and the execution environment. The DSPL supports self-configuration based on coarse-grained modules. We provide a feature-based adaptation mechanism that reduces the effort of computing an optimal configuration at runtime. In a case study, we demonstrate the practicability of our approach and show that a seamless integration of static binding and runtime adaptation reduces the complexity of the adaptation process.