This presentation: http://www.cafeconleche.org/slides/xmlone/london2003/xmlfundamentals
XML in a Nutshell, second edition
Elliotte Rusty Harold and W. Scott Means
O'Reilly & Associates, 2002
ISBN 0-596-00292-0
XML Bible, second edition
Elliotte Rusty Harold
Hungry Minds, 2001
ISBN 0-7645-4760-7