Jie Lu Da Ruan Guangquan Zhang Fuzzy Set Techniques in E-Service Applications. 553-566 2008 Fuzzy Sets and Their Extensions: Representation, Aggregation and Models http://dx.doi.org/10.1007/978-3-540-73723-0_28 series/sfsc/2008-220 db/series/sfsc/sfsc220.html#LuRZ08