In a hierarchical data base, the successive vertical dependencies of records or segments.
在层次型数据库中, 表示数据库元素记录或段的纵向逐次的相关性.
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Hierarchical data has a parent - child relationship that is not naturally represented in a relational database table.
分级数据的父子关系不能在关系数据库表中自然的表示出来.
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