Y. Y. Yao J. P. Zhang Interpreting Fuzzy Membership Functions in the Theory of Rough Sets. 82-89 2000 conf/rsctc/2000 Rough Sets and Current Trends in Computing http://link.springer.de/link/service/series/0558/bibs/2005/20050082.htm db/conf/rsctc/rsctc2000.html#YaoZ00