In Oracle XML DB, XQuery expressions need to be evaluated by SQL/XML functions such as XMLQuery():
[PASSING value-expression [AS identifier]]
[NULL ON EMPTY]
The XMLQuery() function has two required arguments, an XQuery expression and a RETURNING CONTENT statement. The value-expression is used in the PASSING expression to pass in a sequence of XML nodes or atomic values to XQuery. You can assign a name alias to the passed-in XML data using the AS operator. RETURNING CONTENT returns the XQuery output. XMLQuery() can operate on different data sources. Normally, XMLQuery() operates on the following types of XML data sources:
XMLType objects Constructed from ...