Promote-pl: a round-trip engineering process model for adopting and evolving product lines

Process models for software product-line engineering focus on proactive adoption scenarios---that is, building product-line platforms from scratch. They comprise the two phases domain engineering (building a product-line platform) and application engineering (building individual variants), each of which defines various development activities. Established more than two decades ago, these process models are still the de-facto standard for steering the engineering of platforms and variants. However, observations from industrial and open-source practice indicate that the separation between domain and application engineering, with their respective activities, does not fully reflect reality. For instance, organizations rarely build platforms from scratch, but start with developing individual variants that are re-engineered into a platform when the need arises. Organizations also appear to evolve platforms by evolving individual variants, and they use contemporary development activities aligned with technical advances. Recognizing this discrepancy, we present an updated process model for engineering software product lines. We employ a method for constructing process theories, building on recent literature as well as our experiences with industrial partners to identify development activities and the orders in which these are performed. Based on these activities, we synthesize and discuss the new process model, called promote-pl. Also, we explain its relation to modern software-engineering practices, such as continuous integration, model-driven engineering, or simulation testing. We hope that our work offers contemporary guidance for product-line engineers developing and evolving platforms, and inspires researchers to build novel methods and tools aligned with current practice.