This presentation: http://www.cafeconleche.org/slides/sd2004west/xmlfundamentals
XML in a Nutshell, second edition
Elliotte Rusty Harold and W. Scott Means
O'Reilly & Associates, 2002
ISBN 0-596-00292-0
XML 1.1 Bible
Elliotte Rusty Harold
Hungry Minds, 2004
ISBN 0-7645-4986-3