schema augmentation?

 
  We have a schema that validates the following elements:
  
  
  <DateTime>
   <Date>20051017</Date>
   <Time>230001</Time>
  </DateTime>
  
  DateTime must contain one Date and one Time element
  Date must match a pattern
  Time must match a pattern
  
  
  We have a client who wishes to add to our definition of the DateTime element:
  
  <DateTime>
   <Date>20051017</Date>
   <Time>230001</Time>
   <Zone>EST</Zone>
  </DateTime>
  
  
  Can this be done with schema without the client altering our schema?
  Could this be done with namespaces?
  
  
  
  
  <DateTime xmlns="local">
   <Date>20051017</Date>
   <Time>230001</Time>
  </DateTime>
  
  
  
  <DateTime xmlns="client">
   <Date>20051017</Date>
   <Time>230001</Time>
   <Zone>EST</Zone> <!-- the client xsd would simply augment the local xsd -->
  </DateTime>
  
  

		
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