Xml xsd element restriction using another element?

This is not possible in XML schema. You cannot have cross-element constraints of this sort, you will have to use another language (Schematron, XQuery, etc) or write code.

Looks like you can do it with XSD 1.1, but it is not released and there are no implementations of it I can use.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.