At the moment a working group at the W3C to create a query language for XML databases or documents.
The current work can be found at: http://www.w3.org/XML/Query
XQuery, as it is commonly called, is a kind of SQL for XML data(bases). It is tightly connected to XPath 2.0 and XSLT 2.0.
At the moment no Tcl implementation exists, partially because XQuery uses XML Schema Validation extensivly. It would probably be quite easy to provide a Tcl interface to a XQuery engine like Saxon [L1 ] or the Galax [L2 ].
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