There can be only one root node and all others nodes have to be organized in a hierarchical form.
只有一个根节点，所有其它节点都必须以分层形式来组织。
This enables well-formed XML documents to be stored in their hierarchical form within columns of Siebel tables.
这使得可以将格式良好的XML文档以其自身固有的分层格式存储在Siebel表列中。
Arguably the most significant advance of the GUI menu was this retreat from the hierarchical form into monocline grouping.
可以证明，图形用户界面菜单最重要的进步是放弃了层次关系，而改为单层分组。
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