If you're looking to do some simple XQuery work, Berkeley DB XML (BDBXML) seems to be a good answer.

The XML that I was loading into the DB has a default namespace. For example:

<?xml version="1.0" encoding="UTF-8"?>
<item xmlns="http://example.org/item"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://example.org/item item.xsd">
    <size>...</size>
    ...
<item>

Unfortunately BDBXML does not allow one to declare the default namespace:

xmlQueryContext.setNamespace("", "http://example.org/item");

You must bind a prefix to the namespace and use that in any XQuery / XPath:

[code]
xmlQueryContext.setNamespace("i", "http://example.org/item");

[query]
/i:item/i:size