Variability modelling challenges from the trenches of an open source product line re-engineering project

Variability models, feature diagrams ahead, have be-come commonplace in the software product lines engi-neering literature. Whereas ongoing research keeps im-proving their expressiveness, formalisation and automation, more experience reports on their usage in real projects are needed. This paper describes some challenges encountered during the re-engineering of PloneMeeting, an Open Source software family, into a software product line. The main challenging issues we could observe were (i) the ambigu-ity originating from implicit information (missing defini-tions of feature labels and unclear modelling viewpoint), (ii) the necessity of representing spurious features, (iii) the difficulty of making diagrams and constraints resistant to change, and (iv) the risks of using feature attributes to rep-resent large sets of subfeatures. Our study reveals the lim-itations of current constructs, and calls for both language and methodological improvements. It also suggests further comparative evaluations of modelling alternatives.