Article 1 (EC Decision) "Universal Business Language version 2.1 developed by the Organization for the Advancement of Structured Information Standards is eligible for referencing in public procurement.":

http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=OJ:JOL_2014_315_R_00…

OASIS Universal Business Language v2.1 defines a generic XML interchange format for procurement and transportation electronic business documents that can be restricted or extended to meet the requirements of particular industries:

http://docs.oasis-open.org/ubl/os-UBL-2.1/UBL-2.1.html

UBL 2.1 defines 65 different document types such as purchase order, invoice, waybill, transportation status.  All documents are based on a common library of business objects with which one can create their own document types to complement the UBL document types.