XQuery is the language that designed to query XML data. It is built on XPath expressions which are being used to navigate through elements and attributes in an XML document.
The XQuery Update Facility is a relatively small extension of the XQuery language which provides convenient means of modifying XML documents or data. As of March 14, 2008, the XQuery Update Facility specification has become a "Candidate Recommendation", which means it is now pretty stable.
...