Phil Greenwood Ruzanna Chitchyan Awais Rashid Joost Noppen Franck Fleurey Arnor Solberg Modelling adaptability and variability in requirements. 343-344 2011 RE http://dx.doi.org/10.1109/RE.2011.6051667 conf/re/2011 db/conf/re/re2011.html#GreenwoodCRNFS11