Jean-Christophe Trigaux

Feature Diagrams: A Survey and a Formal Semantics

Feature diagrams (FD) are a family of popular modelling languages used for engineering requirements in software product lines. FD were first introduced by Kang as part of the FODA (feature oriented domain analysis) method back in 1990, Since then, various extensions of FODA FD were devised to compensate for a purported ambiguity and lack of precision and expressiveness. However, they never received a proper formal semantics, which is the hallmark of precision and unambiguity as well as a prerequisite for efficient and safe tool automation, In this paper, we first survey FD variants. Subsequently, we generalize the various syntaxes through a generic construction called free feature diagrams (FFD). Formal semantics is defined at the FFD level, which provides unambiguous definition for ail the surveyed FD variants in one shot. All formalisation choices found a clear answer in the original FODA FD definition, which proved that although informal and scattered throughout many pages, it suffered no ambiguity problem. Our definition has several additional advantages: it is formal, concise and generic. We thus argue that it contributes to improve the definition, understanding, comparison and reliable implementation of FD languages

Generic semantics of feature diagrams

Feature Diagrams (FDs) are a family of popular modelling languages used to address the feature interaction problem, particularly in software product lines, FDs were first introduced by Kang as part of the FODA (Feature-Oriented Domain Analysis) method back in 1990. Afterwards, various extensions of FODA FDs were introduced to compensate for a purported ambiguity and lack of precision and expressiveness. However, they never received a formal semantics, which is the hallmark of precision and unambiguity and a prerequisite for efficient and safe tool automation. The reported work is intended to contribute a more rigorous approach to the definition, understanding, evaluation, selection and implementation of FD languages. First, we provide a survey of FD variants. Then, we give them a formal semantics, thanks to a generic construction that we call Free Feature Diagrams (FFDs). This demonstrates that FDs can be precise and unambiguous. This also defines their expressiveness. Many variants are expressively complete, and thus the endless quest for extensions actually cannot be justified by expressiveness. A finer notion is thus needed to compare these expressively complete languages. Two solutions are well-established: succinctness and embeddability, that express the naturalness of a language. We show that the expressively complete FDs fall into two succinctness classes, of which we of course recommend the most succinct. Among the succinct expressively complete languages, we suggest a new, simple one that is not harmfully redundant: Varied FD (VFD). Finally, we study the execution time that tools will need to solve useful problems in these languages.

Evaluating formal properties of feature diagram languages

Feature diagrams (FDs) are a family of popular modelling languages, mainly used for managing variability in software product lines. FDs were first introduced by Kang et al. as part of the feature-oriented domain analysis (FODA) method back in 1990. Since then, various extensions of FODA FDs were devised to compensate for purported ambiguity and lack of precision and expressiveness. Recently, the authors surveyed these notations and provided them with a generic formal syntax and semantics, called free feature diagrams (FFDs). The authors also started investigating the comparative semantics of FFD with respect to other recent formalisations of FD languages. Those results were targeted at improving the quality of FD languages and making the comparison between them more objective. The previous results are recalled in a self-contained, better illustrated and better motivated fashion. Most importantly, a general method is presented for comparative semantics of FDs grounded in Harel and Rumpes guidelines for defining formal visual languages and in Krogstie et al.s semiotic quality framework. This method being actually applicable to other visual languages, FDs are also used as a language (re)engineering exemplar throughout the paper.

Comparative semantics of Feature Diagrams: FFD vs. vDFD

Feature Diagrams are a popular family of modelling languages used for engineering requirements in software product lines. In our previous research, we advocated the use of formal semantics as an indispensable means to clarify discussions about feature diagrams and to facilitate safe and efficient tool automation. We presented a generic formal semantics for feature diagram languages and criteria to compare them. However, other formal semantics exist. We already informally argued in favour of our semantics which, we think, is more abstract, more concise and not tool dependent. However, some of these claims needed to be further objectified. The purpose of this paper is to compare the semantics proposed by van Deursen and Klint with our own following the methodology of comparative semantics. To be made amenable to comparison, van Deursen and Klints tool-based definition is first recalled and redefined by correcting some minor mistakes. Their semantics is then mapped to ours through an abstraction function. We then proceed to compare the expressiveness, embeddability and succinctness of both approaches. The study tends to confirm our semantic choices as well as our tool-independent methodology. It also demonstrates that van Deursen and Klints language is fully expressive and provides various results likely to help tool developers, especially for implementing model transformations.