validating parser

I apologize if this is not the proper list to post this question. I am
somewhat new to XML.

Does anyone know of a validating parser that will run on Linux and use
an XDR schema?  I have found many that use XSD schemas. I would prefer
to use the schema referenced within the XML document.

thanks

Jeff

Jeffrey P. Besecker
Project Manager
PG Energy
division of Southern Union Co.