A unique reference of the document reference. May point to the tender, call for tenders or related documents like the ESPD response. The cbc:ID of a Call for tenders reference creates a link between the call for tender and the tender.The call for tenders and tenders reference must be a UUID

Namespace
cbc urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2
Data type
Identifier
Rules
Identifier/Error message Flag
PEPPOL-T005-R013
DocumentReference Identifiers MUST be unique.
fatal
PEPPOL-T005-R012
DocumentReference Identifier for a Call for Tender Reference MUST be expressed in a UUID syntax (RFC 4122)
fatal