Prof.Ye Dongyi has pointed out in his paper that the reduction approach proposed by Hu Xiaohua et al.will lead to wrong results under some circumstances.In this paper

we find out through analysis that Ye’s approach is actually positive region reduction

whereas Hu’s approach is to make sure that the boundary regions are kept unchanged.The main difference between the two approaches is that each use a different standard

thus there is no ground to judge which one is correct or wrong.What is more

we clarify the relationship among various reduction standards for decision table

and we also give the relationship between reduction results when there is a strong-week correlation between two reduction standards.