XMI export

I’m trying to understand the XMI files that VP exports from UML2.0.
Does somebody know where can I get the XMI 2.1 Schema of these files?

the XMI is part of the UML specification by the OMG.
So when you go to the OMG page (www.omg.org) and just search for XMI you should find the formal specifications for this.

Best regards