Behaviour interactions among product-line features

A software product line (SPL) is often constructed as a set of features, such that individual products can be assembled from a set of common features and a selection of optional features. Although features are conceptualized, developed, and evolved as separate concerns, it is often the case that, in practice, they interfere with each other -- called a feature interaction. In this paper, we precisely define what it means for one feature to have a behaviour interaction with another feature, where the behaviour of one feature is affected by the presence of another feature. Specifically, we use a form of bisimilarity to define when the behaviour of a feature in isolation differs from its behaviour in the presence of an interacting feature. We also consider the case where features are modelled in a language that allows the specification of intended interactions, and we adapt our use of bisimilarity to provide a formal definition for unintended behaviour interactions.