Matthias Riebisch Detlef Streitferdt Ilian Pashov Modeling Variability for Object-Oriented Product Lines. 165-178 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3013&spage=165 2003 conf/ecoopw/2003 ECOOP Workshops db/conf/ecoopw/ecoopw2003.html#RiebischSP03