Version handling for XML interface

Hi

I'm developing an interface to allow using an application programmatically. The interface includs functions that use XML records as arguments. For example SomeFunc( string inStr ) where inStr is an XML record. I'm using schemas to define the XML records.

My problem is how to keep versions of the XML records, assuming that the function prototypes will not change. Is there any standard? Should I keep a separate schema for each version?

Thanks
Omri