This presentation: http://www.ibiblio.org/xml/slides/xmlonelondon2001/xlinks
XML Base Specification: http://www.w3.org/TR/xmlbase
XInclude Specification: http://www.w3.org/TR/xinclude
XPath Specification: http://www.w3.org/TR/xpath
XML in a Nutshell
Elliotte Rusty Harold and W. Scott Means
O'Reilly & Associates, 2001
ISBN 0-596-00058-8
XPath: http://www.oreilly.com/catalog/xmlnut/chapter/ch09.html
XML Bible, second edition
Elliotte Rusty Harold
Hungry Minds, 2001
ISBN 0-7645-4760-7
XLinks: http://www.ibiblio.org/xml/books/bible/updates/16.html
XPointers: http://www.ibiblio.org/xml/books/bible/updates/17.html