Joachim Bayer Oliver Flege Peter Knauber Roland Laqua Dirk Muthig Klaus Schmid Tanya Widen Jean-Marc DeBaud PuLSE: A Methodology to Develop Software Product Lines. 122-131 1999 SSR http://doi.acm.org/10.1145/303008.303063 db/conf/ssr/ssr99.html#BayerFKLMSWD99