There are two essential places to look for XML information:
http://www.oasis-open.org/cover Robin Cover's page
http://www.ucc.ie/xml Peter Flynn's FAQ
You will find everything there and pointers to everything elsewhere.
P.
Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
net connection
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary
http://www.venus.co.uk/vhg