Steven She

Reverse engineering feature models

Feature models describe the common and variable characteristics of a product line. Their advantages are well recognized in product line methods. Unfortunately, creating a feature model for an existing project is time-consuming and requires substantial effort from a modeler. We present procedures for reverse engineering feature models based on a crucial heuristic for identifying parents - the major challenge of this task. We also automatically recover constructs such as feature groups, mandatory features, and implies/excludes edges. We evaluate the technique on two large-scale software product lines with existing reference feature models--the Linux and eCos kernels--and FreeBSD, a project without a feature model. Our heuristic is effective across all three projects by ranking the correct parent among the top results for a vast majority of features. The procedures effectively reduce the information a modeler has to consider from thousands of choices to typically five or less.

Variability modeling in the real: a perspective from the operating systems domain

Variability models represent the common and variable features of products in a product line. Several variability modeling languages have been proposed in academia and industry; however, little is known about the practical use of such languages. We study and compare the constructs, semantics, usage and tools of two variability modeling languages, Kconfig and CDL. We provide empirical evidence for the real-world use of the concepts known from variability modeling research. Since variability models provide basis for automated tools (feature dependency checkers and product configurators), we believe that our findings will be of interest to variability modeling language and tool designers.

Sample Spaces and Feature Models: There and Back Again

We present probabilistic feature models (PFMs) and illustrate their use by discussing modeling, mining and interactive configuration. PFMs are formalized as a set of formulas in a certain probabilistic logic. Such formulas can express both hard and soft constraints and have a well defined semantics by denoting a set of joint probability distributions over features. We show how PFMs can be mined from a given set of feature configurations using data mining techniques. Finally, we demonstrate how PFMs can be used in configuration in order to provide automated support for choice propagation based on both hard and soft constraints. We believe that these results constitute solid foundations for the construction of reverse engineering tools for software product lines and configurators using soft constraints.

Evolution of the linux kernel variability model

Understanding the challenges faced by real projects in evolving variability models, is a prerequisite for providing adequate support for such undertakings. We study the evolution of a model describing features and configurations in a large product line--the Linux kernel variability model. We analyze this evolution quantitatively and qualitatively. Our primary finding is that the Linux kernel model appears to evolve surprisingly smoothly. In the analyzed period, the number of features had doubled, and still the structural complexity of the model remained roughly the same. Furthermore, we provide an in-depth look at the effect of the kernels development methodologies on the evolution of its model. We also include evidence about edit operations applied in practice, evidence of challenges in maintaining large models, and a range of recommendations (and open problems) for builders of modeling tools.

A Study of Variability Models and Languages in the Systems Software Domain

Variability models represent the common and variable features of products in a product line. Since the introduction of FODA in 1990, several variability modeling languages have been proposed in academia and industry, followed by hundreds of research papers on variability models and modeling. However, little is known about the practical use of such languages. We study the constructs, semantics, usage, and associated tools of two variability modeling languages, Kconfig and CDL, which are independently developed outside academia and used in large and significant software projects. We analyze 128 variability models found in 12 open--source projects using these languages. Our study 1) supports variability modeling research with empirical data on the real-world use of its flagship concepts. However, we 2) also provide requirements for concepts and mechanisms that are not commonly considered in academic techniques, and 3) challenge assumptions about size and complexity of variability models made in academic papers. These results are of interest to researchers working on variability modeling and analysis techniques and to designers of tools, such as feature dependency checkers and interactive product configurators.

Generating range fixes for software configuration

To prevent ill-formed configurations, highly configurable software often allows defining constraints over the available options. As these constraints can be complex, fixing a configuration that violates one or more constraints can be challenging. Although several fix-generation approaches exist, their applicability is limited because (1) they typically generate only one fix, failing to cover the solution that the user wants; and (2) they do not fully support non-Boolean constraints, which contain arithmetic, inequality, and string operators. This paper proposes a novel concept, range fix, for software configuration. A range fix specifies the options to change and the ranges of values for these options. We also design an algorithm that automatically generates range fixes for a violated constraint. We have evaluated our approach with three different strategies for handling constraint interactions, on data from five open source projects. Our evaluation shows that, even with the most complex strategy, our approach generates complete fix lists that are mostly short and concise, in a fraction of a second.

Efficient synthesis of feature models

Variability modeling, and in particular feature modeling, is a central element of model-driven software product line architectures. Such architectures often emerge from legacy code, but, unfortunately creating feature models from large, legacy systems is a long and arduous task. We address the problem of automatic synthesis of feature models from propositional constraints. We show that this problem is NP-hard. We design efficient techniques for synthesis of models from respectively CNF and DNF formulas, showing a 10- to 1000-fold performance improvement over known techniques for realistic benchmarks. Our algorithms are the first known techniques that are efficient enough to be applied to dependencies extracted from real systems, opening new possibilities of creating reverse engineering and model management tools for variability models. We discuss several such scenarios in the paper.

Variability mechanisms in software ecosystems

Abstract Context Software ecosystems are increasingly popular for their economic, strategic, and technical advantages. Application platforms such as Android or iOS allow users to highly customize a system by selecting desired functionality from a large variety of assets. This customization is achieved using variability mechanisms. Objective Variability mechanisms are well-researched in the context of software product lines. Although software ecosystems are often seen as conceptual successors, the technology that sustains their success and growth is much less understood. Our objective is to improve empirical understanding of variability mechanisms used in successful software ecosystems. Method We analyze five ecosystems, ranging from the Linux kernel through Eclipse to Android. A qualitative analysis identifies and characterizes variability mechanisms together with their organizational context. This analysis leads to a conceptual framework that unifies ecosystem-specific aspects using a common terminology. A quantitative analysis investigates scales, growth rates, and—most importantly—dependency structures of the ecosystems. Results In all the studied ecosystems, we identify rich dependency languages and variability descriptions that declare many direct and indirect dependencies. Indirect dependencies to abstract capabilities, as opposed to concrete variability units, are used predominantly in fast-growing ecosystems. We also find that variability models—while providing system-wide abstractions over code—work best in centralized variability management and are, thus, absent in ecosystems with large free markets. These latter ecosystems tend to emphasize maintaining capabilities and common vocabularies, dynamic discovery, and binding with strong encapsulation of contributions, together with uniform distribution channels. Conclusion The use of specialized mechanisms in software ecosystems with large free markets, as opposed to software product lines, calls for recognition of a new discipline—variability encouragement.

Range Fixes: Interactive Error Resolution for Software Configuration

To prevent ill-formed configurations, highly configurable software often allows defining constraints over the available options. As these constraints can be complex, fixing a configuration that violates one or more constraints can be challenging. Although several fix-generation approaches exist, their applicability is limited because (1) they typically generate only one fix or a very long fix list, difficult for the user to identify the desirable fix; and (2) they do not fully support non-Boolean constraints, which contain arithmetic, inequality, and string operators. This paper proposes a novel concept, range fix, for software configuration. A range fix specifies the options to change and the ranges of values for these options. We also design an algorithm that automatically generates range fixes for a violated constraint. We have evaluated our approach with three different strategies for handling constraint interactions, on data from nine open source projects over two configuration platforms. The evaluation shows that our notion of range fix leads to mostly simple yet complete sets of fixes, and our algorithm is able to generate fixes within one second for configuration systems with a few thousands options and constraints.

Usage scenarios for feature model synthesis

Feature models are menu-like hierarchies of features (i.e., configuration options) used in variability-rich software. Feature models have many applications such as domain analysis, describing design and implementation constraints in software, or for product configuration. The many applications of feature models have given rise to a wide range of scenarios involving feature model synthesis. Feature model synthesis is the process of building a feature model for a given set of features and their allowed combinations, expressed as feature dependencies or feature configurations. We describe and classify software re-engineering scenarios involving feature model synthesis found in literature and industry. We analyze these scenarios to derive requirements for feature model synthesis techniques.