At the policy model conference call on jan28-02, I agreed to look into the XML Schema to see if it supported arithmetic operators for expressions. I have investigated this and also verified with Eve Maler. XML Schema provides no such support for operators. So either XACML has to define it itself or borrow from MathML (which Eve Maler pointed out to me). It is my understanding that Schematron can be used to attach businesslevel constraints ( rules ) to schema but I have not looked into this. I won't be looking into this any further and should be assigned to a champion. -- Sekhar