A document such as that saved from Google earth defines the URI for the default namespace:
<kml xmlns="http://earth.google.com/kml/2.0">
...
</kml>
Simply trying to access the nodes in this document will not work:
//Placemark[name='arnolfine']
produces no output.
To access the nodes in the default namespace, you must declare a namespace in the XQuery with the same URI
as that referenced in the declaration in the root element.
declare namespace a = "http://earth.google.com/kml/2.0";
and reference the nodes as
//a:Placemark[a:name='Arnolfine']
Now returns the selected node.
Namespaces divide the filestore so that Placemark nodes in another document with a different namespace will not be located by the query above.