A systematic mapping study on software product line evolution: From legacy system reengineering to product line refactoring

Software product lines (SPLs) are used in industry to develop families of similar software systems. Legacy systems, either highly configurable or with a story of versions and local variations, are potential candidates for reconfiguration as SPLs using reengineering techniques. Existing SPLs can also be restructured using specific refactorings to improve their internal quality. Although many contributions (including industrial experiences) can be found in the literature, we lack a global vision covering the whole life cycle of an evolving product line. This study aims to survey existing research on the reengineering of legacy systems into SPLs and the refactoring of existing SPLs in order to identify proven approaches and pending challenges for future research in both subfields. We launched a systematic mapping study to find as much literature as possible, covering the diverse terms involved in the search string (restructuring, refactoring, reengineering, etc. always connected with SPLs) and filtering the papers using relevance criteria. The 74 papers selected were classified with respect to several dimensions: main focus, research and contribution type, academic or industrial validation if included, etc. We classified the research approaches and analyzed their feasibility for use in industry. The results of the study indicate that the initial works focused on the adaptation of generic reengineering processes to SPL extraction. Starting from that foundation, several trends have been detected in recent research: the integrated or guided reengineering of (typically object-oriented) legacy code and requirements; specific aspect-oriented or feature-oriented refactoring into SPLs, and more recently, refactoring for the evolution of existing product lines. A majority of papers include academic or industrial case studies, though only a few are based on quantitative data. The degree of maturity of both subfields is different: Industry examples for the reengineering of the legacy system subfield are abundant, although more evaluation research is needed to provide better evidence for adoption in industry. Product line evolution through refactoring is an emerging topic with some pending challenges. Although it has recently received some attention, the theoretical foundation is rather limited in this subfield and should be addressed in the near future. To sum up, the main contributions of this work are the classification of research approaches as well as the analysis of remaining challenges, open issues, and research opportunities.

► Legacy systems can be reconfigured as product lines using reengineering techniques.
► Software product lines can also be refactored to improve their quality.
► This work is a systematic mapping study of existing research in both fields.
► The 74 papers are classified; challenges and research opportunities are presented.
► Many works include case studies, but only a few provide empirical data.