Abstract: In the fuzzy information system,attribute value is not an uncertain value,it is a membership function.Therefore,differences between objects are aggregated by the ordered weighted averaging (OWA) operator for all the attri-butes,which characterizes the similarity of objects.Then similar degree of objects was defined and the related properties were discussed.According to the similar degree of objects,the membership degree of an object which belongs to lower and upper approximations was given by logic relations and function operations.Finally,experimental results show that the similarity of objects can be accurately characterized by the similar degree of objects.Moreover,every object belonging to the lower and upper approximation sets can be more visually and reasonably described by membership degrees of every object for lower and upper approximations.Meanwhile,the description of the rough set can be more reasonable.

Key words: Fuzzy information system,Rough set,Similar degree,Tolerance relation,Membership degree