On the upper approximations of covering generalized rough sets

The covering generalized rough set is an improvement of Pawlak rough set to deal with more complex practical problems which the latter one cannot handle. However, many basic notions in this theory are not as widely agreeable as in the Pawlak rough set theory. We mainly improve the definition of upper approximation for covering generalized rough sets to make it more reasonable than the existing ones. Thus we set up a framework for the approximation operators of covering rough sets.