A hierarchical variability model for software product lines

Abstract. A key challenge in software product line engineering is to rep-resent solution space variability in an economic, yet easily understand-able fashion. We introduce the notion of hierarchical variability models to describe families of products in a manner that facilitates their modular design and analysis. In this model, a family is represented by a common set of artifacts and a set of variation points with associated variants. A variant is again a hierarchical variability model, leading to a hierar-chical structure. These models, however, are not unique with respect to the families they define. We therefore propose a quantitative measure on hierarchical variability models that expresses the degree to which a vari-ability model captures commonality and variability in a family. Further, by imposing well-formedness constraints, we identify a class of variabil-ity models that, by construction, have maximal measure and are unique for the families they define. For this class of simple families, we pro-vide a procedure that reconstructs their hierarchical variability model. The reconstructed model can be used to drive various static analyses by divide-and-conquer reasoning. Hierarchical variability models strike a balance between the formalism’s expressiveness and the desirable prop-erty of model uniqueness. We illustrate the approach by a small product line of Java classes.