XSD are from this repository : https://github.com/ConnectingEurope/eInvoicing-EN16931/tree/master/ubl/schema
The XML Schema (XSD) of OASIS UBL 2.1 can be downloaded from OASIS. The ZIP file is located at http://docs.oasis-open.org/ubl/os-UBL-2.1/UBL-2.1.zip
