A Novel Method for Upper and Lower Approximation of Class Unions Based on Dominance-matrix

Dominance-based Rough Set Approach (DRSA) is an extension of classical Rough Set Theory (RST) to deal with inconsistent problems. Approximation of class unions is the key method of DRSA and it is a very complex computing job. However, the formal work within DRSA only proposed relative definitions of the concept including approximation of class unions, but no efficient algorithm has been given. So we can only use the original definition to get the approximation of class unions. As a result, it is very complex, and it requires a considerable amount of computing time. In this paper a dominance-matrix is developed and a new method is presented for the approximation of class unions based on dominance-matrix. It simplifies the calculation process and decreases the computing time.