Xena normalises office type documents using OpenOffice.org. openOffice.org does not use XML schema to define its document formats, rather it uses Document Type Definitions (DTDs).
You can view these DTDs in the OpenOffice install directory in the {install path}\share\dtd directory. For a default Windows install of OpenOffice.org this would be c:\program files\OpenOffice.org {version}\share\dtd.
For more information, see the OpenOffice.org help.