General Mode of Operation

The software was created under the assumption that many small businesses create their invoices with the help of spreadsheet software like LibreOffice. That means that the invoice data is already available as structured data.

All that was left to be done was to map the input spreadsheet data to elements in the output XML of the electronic invoice. Because there are multiple supported output XML formats, it makes sense to first map the input data into a general internal format and then render the data into the desired output format.

The internal format chosen is largely equivalent to that of Peppol UBL. The advantages are:

• The documentation is browsable and relatively easy to understand.
• It is generated from data (see https://github.com/OpenPEPPOL/peppol-bis-invoice-3) that also allows generating JSON schema definitions.
• From these JSON schema definitions, it is possible to generate large parts of the code of E-Invoice-EU.

As a result, it is easy to keep the implementation up-to-date with the current standards by Peppol.