Re: only one of the element is req but not both...

Hi Srivanas

These sort of combined constraints cannot be dealt with very
well in XSD. Why don't you look into e.g Schematron:

http://www.ascc.net/xml/resource/schematron/schematron.html

I am finding I can manage some quite difficult constraints using 
Schematron in my project although the syntax is a bit difficult at 
first. I struggled with KEY/KEYREF in XSD quite a lot and am now 
replacing these with Schematron rules, which are more flexible 
and powerful and allow me to specify my own error messages which 
means my users may even be able to understand them ! :-)
 
cheers
Gaz