Andreas Birk 0001 Gerald Heller Isabel John Klaus Schmid Thomas von der Maßen Klaus Müller Product Line Engineering: The State of the Practice. 52-60 2003 20 IEEE Software 6 http://doi.ieeecomputersociety.org/10.1109/MS.2003.1241367 db/journals/software/software20.html#BirkHJSMM03