Abstract: Dominance-based rough set approach (DRSA) is an extension of classical rough set theory (RST). Approximation of class unions is a very important approach in DRSA. Aiming at the disadvantage of the classical method, this paper presents a new methodology for approximation of class unions based on dominance-matrix. It only needs to calculate the dominance-matrix and does not need to consider the preference relations one by one. Thus it greatly simplifies the process and decreases the computing complex by k times(where k is the number of the decision classes). Besides it is intuitive and efficient. The example illustrates its feasibility and efficiency.

Key words: Rough set theory, Dominance-based rough set approach (DRSA), Approximation of class unions, Dominance-matrix

摘要： 摘 要：DRSA(Dominance-based Rough Set Approach)是经典粗糙集理论在支配关系下的扩展，而类合集近似是DRSA中非常重要的概念与方法。传统的方法是利用原始的定义来求取类合集的上下近似，针对其计算复杂的缺点，该文提出了一种基于支配矩阵的类合集近似新方法，不仅将计算复杂度降到约1/k倍（k为决策类的个数），而且简捷直观。最后的实例证明了新方法的有效性及可行性。

关键词: 粗糙集理论, DRSA, 类合集近似, 支配矩阵