Extracting a namespace prefix

Question

Hi,
I have the following document
<ns4:product xmlns:ns1="www.abc.com" xmlns:ns2="www.def.com" xmlns:ns3="www.ghi.com" xmlns:ns4="www.jkl.com">
<ns4:productline>Widget</ns4:productline>
</ns4:product>
I'm trying to find a SQL function which will enable me to extract the namespace prefix with the value "www.jkl.com". This is so that I can then use the prefix as part of the xpath expression to search for an element value in the document eg. extractvalue('/ns4:product/ns4:productline')
Thanks

Answer 1

Hi,
This one's tricky, so tricky that I think it's not possible using Oracle built-in XML DML functions.
Even XQuery Update cannot do it (for now) because, likewise, the prefix is always redeclared at child level.
The only thing I can think of is XSLT (or maybe DOM manipulation) :
SQL> select xmlserialize(document
  2           xmltransform(
  3             xmltype('<A xmlns="namespace" xmlns:def="myns_namespace"/>')
  4           , xmltype(
  5  '<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  6     xmlns:def="myns_namespace"
  7     xmlns:ns0="namespace">
  8    <xsl:template match="ns0:A">
  9      <xsl:copy>
10        <xsl:element name="def:B"/>
11      </xsl:copy>
12    </xsl:template>
13  </xsl:stylesheet>')
14         )
15        indent
16      )
17  from dual;
XMLSERIALIZE(DOCUMENTXMLTRANSF
<A xmlns="namespace" xmlns:def="myns_namespace">
  <def:B/>
</A>