A hierarchical database stores data in a tree structure; an order record might have every line item underneath it.
层级数据库按照树状结构存储数据，一份订单记录在它的下面可能有每一行一个项。
A hierarchical database stores data in a tree structure; an order record might have every line item underneath it.
层级数据库按照树状结构存储数据，一份订单记录在它的下面可能有每一行一个项。
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