Composing Annotations Without Regret? Practical Experiences Using FeatureC

Software product lines enable developers to derive similar products from a common code base. Existing implementation techniques can be categorized as composition-based and annotation-based, with both approaches promising complementary benefits. However, annotation-based approaches are commonly used in practice despite composition allowing physical separation of features and, thus, improving traceability and maintenance. A main hindrance to migrate annotated systems towards a composition-based product line is the challenging and time consuming transformation task. For a company it is difficult to predict the corresponding costs, and a successful outcome is uncertain. To overcome such problems, a solution proposed by previous work is to use a hybrid approach, utilizing composition and annotation simultaneously. Based on this idea, we introduce a step-wise migration process from annotation-based towards composition-based approaches to lower the adoption barrier of composition. This process itself is independent of used implementation techniques and enables developers to incrementally migrate towards composition. We support our approach with detailed examples by partially migrating a real-world system. In detail, we describe i) our migration process, ii) its application on a real-world system, and iii) discuss practical challenges we faced. We implemented the proposed approach and show that appropriate tool support helps to migrate towards composition-based product lines. Based on the case study, we show that hybrid product lines work correctly and can compete with the performance of the original annotated system. However, the results also illustrate open issues that have to be solved to apply such migrations in practice.