By extending the crisp set X to the fuzzy set F, Dubois and Prade defined the notion of rough fuzzy sets (a special case of fuzzy rough sets), and fuzzy rough sets with respect to the fuzzy relation R.

• 通过将近似对象由经典集合X推广到模糊集合F,Dubois和Prade定义了粗糙模糊集的概念(模糊粗糙集的一个特殊情形),又引入模糊关系R得到模糊粗糙集的概念。