Documents
Document nodes represent entire XML documents in the XQuery data model. When an input document is opened using the doc function, a document node is returned. The document node should not be confused with the outermost element node, which is its child.
Not all XML data selected or constructed by queries has a document node at its root. Some implementations will allow you to query XML fragments, such as an element or a sequence of elements that are not part of a document. When XML is stored in a relational database, it often holds elements without any containing document. It is also possible, using element constructors, to create result elements that are not part of a document.
The root function can be used to determine whether a node is part of a document. It will return the root of the hierarchy, whether it is a document node or simply a standalone element.
Document Nodes and the Data Model
A document node is the root of a node hierarchy, and therefore has no parent. The children of a document node are the comments and processing instructions that appear outside of any element, and the outermost element node. For example, the document shown in Example 21-4 would be represented by a single document node that has two children: the xml-stylesheet processing-instruction node and the businessDocument element node.
The string value of a document node is the string value of all its text node descendants, concatenated together. In Example 21-4, that would simply be 2006-10-15 ...
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