This paper extends the Pawlak rough set model to double universe of discourse. The equivalence relation on a double universe of discourse is defined as well as the information system and rough set on double universe. Furthermore, a constraint relation is introduced to deal with the structures within the double universe of discourse, and thus the definitions with respect to rough set model on double universe of discourse are refined and the properties about lower and upper approximations are proved. Finally, the definition of rough graph is presented as an example of rough set model with double universe of discourse.
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