UBL
UBL (Universal Business Language) is an XML syntax for business documents, one of the two ways an EN 16931 invoice can be expressed.
UBL defines the actual XML tags an invoice uses, such as the elements for a line item or a tax total. It is the syntax behind Peppol BIS and one of the two syntaxes allowed under EN 16931, the other being CII.
A team rarely cares which syntax an invoice arrives in, only that the data comes through cleanly. But interoperability depends on tools handling both.
Cortena parses UBL invoices directly and codes them like any other document.