http://sleepycat.com/products/xml.shtml [url]

Might be of use:

Berkeley DB XML is the native XML database engine for your product. Berkeley DB
XML provides XQuery access into a database of document containers. XML documents
are stored and indexed in their native format using Berkeley DB as the
transactional database engine. Berkeley DB XML is not a client/server database
management system; it is a C++ library linked into your application.....