TSUBL uses the standard UBL 2.0 XSD. You can download it from here:

http://docs.oasis-open.org/ubl/os-UBL-2.0/xsd/

or

http://ubl.xml.org/wiki/ubl-specifications


You find a general introduction to UBL 2.0 here:

http://docs.oasis-open.org/ubl/os-UBL-2.0/UBL-2.0.html



