Variability models, feature diagrams ahead, have become
commonplace in the software product lines engineering
literature. Whereas ongoing research keeps improving
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 ambiguity
originating from implicit information (missing definitions
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 represent
large sets of subfeatures. Our study reveals the limitations
of current constructs, and calls for both language
and methodological improvements. It also suggests further
comparative evaluations of modelling alternatives.Comisión Interministerial de Ciencia y Tecnología TIN2006-0047