In 1990, Dubois pointed out that these two theories are different mathematical methods in handling two uncertainty(ambiguity and rough) ,and he put forward two kinds of mathematical model of fuzzy rough set and rough fuzzy set.

• 1990年，Dubois等指出两种理论是处理两种不确定性(模糊性和粗糙性)的不同的数学方法，并提出了模糊粗糙集和粗糙模糊集的数学模型。