Flexible features: making feature modules more reusable.

A growing trend in software construction advocates the encapsulation of software building blocks as features which better match the specification of requirements. As a result, programmers find it easier to design and compose different variations of their systems. Feature-oriented programming (FOP) is the research domain that targets this trend. We argue that the state-of-the-art techniques for FOP have shortcomings because they specify a feature as a set of building blocks rather than a transition that has to be applied on a software system in order to add that feature's functionality to the system. We propose to specify features as sets of first-class change objects which can add, modify or delete building blocks to or from a software system. We evaluate this approach by implementing a simple text editor in a feature-oriented way and use the implementation to produce four different program variations. This shows that our approach contributes to FOP on three levels: expressiveness, composition verification and bottom-up feature-oriented development.