(Universal Business Language) A rulebook for electronic business documents. Under development by OASIS, UBL is an XML specification that defines a set of rules (XML schemas) for drawing up electronic messages to represent business documents used in international trade, such as purchase orders, acknowledgements and invoices. It is closely related to the organization's ebXML standard, but is based on cXML (Commerce XML), an early XML-based system for electronic commerce developed by a consortium led by Ariba and Sterling Commerce.