On the modularity of feature interactions

Abstract

Feature modules are the building blocks of programs in software product lines (SPLs). A foundational assumption of feature-based program synthesis is that features are composed in a predefined sequence called a natural order. Recent work on virtual separation of concerns reveals a new model of feature interactions that shows that feature modules can be quantized as compositions of smaller modules called derivatives. We present this model and examine some of its consequences, namely, that (1) a given program can be reconstructed by composing features in any order, and (2) the contents of a feature module (as expressed as a composition of derivatives) is determined automatically by a feature order. We show that different orders allow one to adjust the contents of a feature module to isolate and study the impact of interactions that a feature has with other features. We also show the utility of generalizing safe composition (SC), a basic analysis of SPLs that verifies program type-safety, to demonstrate that every legal composition of derivatives (and thus any composition order of features) produces a type-safe program, which is a much stronger SC property.