Abstract: We proposed two different types of dominance relations in set-valued information systems by the distribution of set-valued when all attributes were considered as criterions, and generalized the dominance relations in classical information systems. The judgment of knowledge reduction and relative reduction of each object were studied for two types of dominance relations in set valued information systems, from which we defined discernibility function based on discernibility matrix, and got approach computing knowledge reduction and relative reduction of each object.

Key words: Set valued information systems, Dominance relation, Discernibility function, Knowledge reduction