XPath with XML Schema

Question

Is there any way of finding out the namespace prefix if there is one, from a DOMParser instance or a XMLDocument instance?
I have a DOMParser instance and I don't know whether there is a namespace specification in it. If there is, I need to know what it is so I can update my XPath expressions to use the appropriate prefix.
I have tried the XMLDocument.getNamespace function but it doesn't seem to be implemented (or it is depricated).
Any help would be greatly appreciated.

Answer 1

You're right on track with the namespaces hunch.
XPath 1.0 does not provide the ability to search on the default namespace.
That is, even if you document looks like this:<foo xmlns="urn:bar"/>you cannot use any compliant XPath 1.0 implementation to find the <foo> element with the pattern /foo, since in XPath 1.0 /foo finds the <foo> element that is the child of the root with a null namespace URI.
In the example above, the namespace uri of the <foo> element is urn:bar, so in particular it's not null.
With XPath 1.0, you need to specifically qualify the foo element with a namespace prefix that is bound to the same namespace URI as your default namespace.
So, your XPath would need to look like /xxx:foo where xxx is an arbitrary namespace prefix associated with the urn:bar namespace URI.
The selectNodes, selectSingleNode, and valueOf methods all have an overloading which takes an instance of the oracle.xml.parser.v2.NSResolver interface as the 2nd argument. This argument is used to resolve what namespace prefixes found in the XPath search string map to.
To implement the NSResolver interface, you need only implement a single method:
String resolveNamespacePrefix(String prefix);
In the example above, this method would return the string "urn:bar" when passed the prefix string "xxx" so that the XPath of /xxx:foo would match the <foo> element with urn:bar namespace uri in the example document above.
Steve Muench
Development Lead, Oracle XSQL Pages Framework
Lead Product Manager for BC4J and Lead XML Evangelist, Oracle Corp
Author, Building Oracle XML Applications
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