EN 16931 extension

An extension adds information to the European e-invoice without breaking compatibility with the EN 16931 core.

Definition

EN 16931 defines a core invoice semantic model: a common baseline of data elements. An extension is a superset that adds information elements beyond that core to meet a specific need, such as an industry sector or a national obligation.

Extension vs CIUS

The standard distinguishes two ways to adapt the core:

• a CIUS (Core Invoice Usage Specification) restricts the core: it makes fields mandatory or forbids them, but adds nothing;
• an extension widens the core: it adds new elements not foreseen by the base model.

In both cases the result must stay compatible with the core business rules.

Good to know

A well-designed extension must never contradict a core BR-* rule: a receiver that understands only the core invoice should be able to ignore the added elements without rejecting the invoice. Factur-X / ZUGFeRD illustrate this with profiles ranging from the core (EN 16931) up to an Extended profile.