items as nodes or atomic values

[Smith, Donald T.]

This may be a well-worn question. If so, please point me to the location
of the discussion. Otherwise. . .

 

I'm thinking through the XQuery/XPath data model. The last paragraph in
section 3.0 has me puzzling: "The data model also supports values that
are not nodes. Examples of these are sequences of atomic values
<http://www.w3.org/TR/2007/REC-xpath-datamodel-20070123/#dt-atomic-value
#dt-atomic-value> , or sequences mixing nodes and atomic values. These
are necessary to be able to represent the results of intermediate
expressions in the data model during expression processing."

 

I'm accustomed, from XPath 1.0,  to thinking of trees of nodes, so I'm
not quite getting what it means to have items in sequences that are
either nodes or atomic values. Since an atomic value is a string that
conforms to an atomic type, atomic types are schema-defined, and nodes
may or may not have schema-defined datatypes, I don't understand the
case where an atomic type would not be associated with - and so
represented by -- a node. In other words, I can't image a XQuery/XPath
sequence as anything other than a node tree, which clearly shows I'm
still in XPath 1.0 land.

 

The last line I quoted above indicates that this whole issue arises from
something that goes on during expression processing, so perhaps this is
an issue that only matters to those who write XQuery/XPath engines. At
any rate, if anyone can clarify this issue for me, I'd appreciate it.

 

Don Smith

Information Architect

American Airlines

817-967-0310

 

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