Data modelling will be using XML as Billing BIS3
Background
Data modelling in Open PEPPOL has been done using Gefeg FX. FX provides significant support for consistency in the model and for publishing the results but has a high learning curve and as requires a paid user license. Both make it difficult to add experts to the team working on the models who are usually contributing their time to OpenPEPPOL work.
The Billing BIS 3 edited the data models in an XML tool that is being developed as an open source tool by DIFI. Working with the tool is familiar to those who have experience with editing XML in text editors, it allows storing the data models in GitHub in the same way as other documentation. On the other hand it is not fully developed and dependent on resourcing although that is currently being provided by Difi. The tool may also require more attention to the consistency in the models.
The decision is to use the XML tool mainly because of its lower learning curve and open source availability.