Introduction to DTD
Xmlfiles.com provides web developers with a basic introduction to programming in xml, xml dtd, xml dom, xml xsl, xml rss and asp.net. learn how to create basic xml programs from xmlfile.com's expert tutorials and example code.
http://xmlfiles.com/dtd/dtd_intro.asp
Microsoft XML FAQ
Microsoft XML FAQ
http://msdn.microsoft.com/library/default.asp?url=/nhp/default.asp?contentid=28000438
Simple XQL Tutorial
Simple XQL Tutorial
http://www.ibiblio.org/xql/xql-tutorial.html