key and keyref to express dependency

hi everybody,
   i really don't find the W3C SChema specification clear, and have a question:
can we express in the W3C Schema that the presence of an element A depends
en the presence of an element B?
i thought about key and keyref elements,but i doubt they just impose
equality!
thank you

Received on Wednesday, 5 June 2002 05:45:10 UTC