拟单层覆盖是形式化表示包含缺省值的离散信息表一种有效的方式,同时它也是离散化连续值时,包容误分类对象的理想的数学模型。因为拟单层覆盖是极小且精确的,所以拟单层覆盖上的近似算子较一般的覆盖粗糙近似算子更为特殊。从集合及点集两个角度定义了四种近似算子,并在讨论其性质的基础上,也讨论了这四种近似算子之间的关系。 Quasi-single-layer coverage is an effective way to formally represent a discrete information table containing default values, and it is also an ideal mathematical model that tolerates misclassification objects when discretizing continuous values. Because the quasi-single-layer coverage is extremely small and accurate, the approximate operators on the quasi-single-layer cover are more special than the general overlay rough approximation operators. Four kinds of approximation operators are defined from the point of collection and point set. Based on the discussion of their properties, the relations among these four approximation operators are also discussed.