Section: New Results

Results on Variability Modeling and Engineering

Engineering Interactive Systems

In agreement with our permanent effort to validate the techniques we propose on real use cases in various domains, we applied seminal MDE to interactive systems engineering. This led to two collaborations. The first one has been conducted with 3D Collaborative Virtual Environments (3D CVE) researchers. Despite the increasing use of 3D CVE, their development is still a cumbersome task. The various concerns to consider (distributed system, 3D graphics, etc.) complexify their development as well as their evolution. We propose to leverage MDE for developing 3D CVEs [45] . We have shown how a 3D CVE framework benefits from a DSL we built using state-of-the-art MDE technologies. The benefits are multiple: 3D CVEs designers can focus on the behavior of their virtual objects without bothering with distributed and graphics features; configuring the content of 3D CVEs and their deployment on various software and hardware platforms can be automated through code generation.

The second collaboration is international and has been conducted with software visualization researchers. Current metamodel editing tools are based on standard visualization and navigation features, such as physical zooms. However, as soon as metamodels become larger, navigating through large metamodels becomes a tedious task that hinders their understanding. In this work, we promote the use of model slicing techniques  [102] to build visualization techniques dedicated to metamodels [37] . This approach is implemented in a metamodel visualizer, called Explain .

Variability management in regulatory requirements and system engineering

Nuclear power plants are some of the most sophisticated and complex energy systems ever designed. These systems perform safety critical functions and must conform to national safety institutions and international regulations. In many cases, regulatory documents provide very high level and ambiguous requirements that leave a wide margin for interpretation. As the French nuclear industry is now seeking to spread its activities outside France, it is but necessary to master the ins and the outs of the variability between countries safety culture and regulations. This sets both an industrial and a scientific challenge to introduce and propose a product line engineering approach to an unaware industry whose safety culture is made of interpretations, specificities, and exceptions. We have developed two contributions within the French R&D project CONNEXION, while introducing variability modeling to the French nuclear industry [66] , [34] .

As part of the VaryMDE project (a bilateral collaboration between Thales and Inria) we have developed techniques to generate counter-examples (also called anti-patterns) of model-based product lines [22] . The goal is to infer (1) guidelines or domain-specific rules to avoid earlier the specification of incorrect mappings (2) testing oracles for increasing the robustness of derivation engines given a modeling language. We have applied the approach in the context of a real industrial scenario with Thales involving a large-scale metamodel.

Handling testing challenges in product line engineering

Testing techniques in industry are not yet adapted for product line engineering (PLE).

We have developed original contributions to adapt model-based testing for PLE [65] , [63] , [13] . We equip usage models, a widely used formalism in MBT, with variability capabilities. Formal correspondences are established between a variability model, a set of functional requirements, and a usage model. An algorithm then exploits the traceability links to automatically derive a usage model variant from a desired set of selected features. The approach is integrated into the MBT tool MaTeLo and is currently used in industry.

We have also developed a variability-based testing approach to derive video sequence variants. The ideas of our VANE approach are i) to encode in a variability model what can vary within a video sequence; ii) to exploit the variability model to generate testable configurations; iii) to synthesize variants of video sequences corresponding to configurations. VANE computes T-wise covering sets while optimizing a function over attributes [50] , [25] .

Reverse engineering variability models

We have developed automated techniques and a comprehensive environment for synthesizing feature models from various kinds of artefacts (e.g. propositional formula, dependency graph, FMs or product comparison matrices). Specifically we have elaborated a support (through ranking lists, clusters, and logical heuristics) for choosing a sound and meaningful hierarchy [42] . We have performed an empirical evaluation on hundreds of feature models, coming from the SPLOT repository and Wikipedia  [108] . We have showed that a hybrid approach mixing logical and ontological techniques outperforms state-of-the-art solutions (to appear in Empirical Software Engineering journal in 2015 [19] ). Beyond the reverse engineering of variability, our work has numerous practical applications (e.g., merging multiple product lines, slicing a configuration process).

Product comparison matrices

Product Comparison Matrices (PCMs) constitute a rich source of data for comparing a set of related and competing products over numerous features. Despite their apparent simplicity, PCMs contain heterogeneous, ambiguous, uncontrolled and partial information that hinders their efficient exploitations. We have first elaborated our vision and identify research challenges for an exploitation of PCMs when engineering comparators, configurators, or other services [67] .

We have formalized PCMs through model-based automated techniques and developed additional tooling to support the edition and re-engineering of PCMs [43] . 20 participants used our editor to evaluate our PCM metamodel and automated transformations. The empirical results over 75 PCMs from Wikipedia show that (1) a significant proportion of the formalization of PCMs can be automated: 93.11% of the 30061 cells are correctly formalized; (2) the rest of the formalization can be realized by using the editor and mapping cells to existing concepts of the metamodel.

The ASE'2014 paper opens avenues for engaging a community in the mining, re-engineering, edition, and exploitation of PCMs that now abound on the Internet. We have launched an open, collaborative initiative towards this direction http://www.opencompare.org