This presentation: http://www.ibiblio.org/xml/slides/sd2001west/namespaces
XML in a Nutshell
Elliotte Rusty Harold and W. Scott Means
O'Reilly & Associates, 2001
ISBN 0-596-00058-8
XML Bible, second edition
Elliotte Rusty Harold
Hungry Minds, 2001
ISBN 0-7645-4760-7