Electronic invoicing isn't just about sending an invoice digitally. For automatic processing, systems must also understand what data they are receiving, what that data means, and how it is technically structured.
Various standards exist for this purpose.
In Europe, UBL is probably the best-known syntax for structured electronic invoices. But UBL isn’t the only one. Within the European standard EN 16931, UN/CEFACT Cross Industry Invoice—usually abbreviated as CII—is also designated as an official syntax.
CII is used in Germany, among other places, and forms the technical basis for well-known formats such as ZUGFeRD and Factur-X.
This makes CII an important standard within the European e-invoicing landscape, even though the name is less familiar to many finance professionals than UBL or Peppol.
1. What is UN/CEFACT CII?
CII stands for Cross Industry Invoice.
The standard was developed by UN/CEFACT, the United Nations Centre for Trade Facilitation and Electronic Business. UN/CEFACT develops international standards for electronic data exchange with the goal of making trade processes simpler and more interoperable.
The name “Cross Industry Invoice” says a lot about its underlying principle.
CII was not developed for a single specific sector. The standard must be able to support invoice data across a wide range of industries, countries, and commercial processes.
The data is stored in XML.
For example, a CII file can contain information about:
- supplier and customer;
- invoice number and invoice date;
- goods and services;
- quantities and prices;
- discounts and surcharges;
- VAT;
- payment terms;
- bank information;
- order references;
- delivery information;
- and totals.
Just as with UBL, it’s not just about the value itself, but also about the meaning of that value.
2. CII and UBL are two different syntaxes for the same European core invoice
Within European e-invoicing, the distinction between semantics and syntax is important.
EN 16931 describes the semantic model of the European core invoice.
That model specifies what business information an electronic invoice contains and what that information means.
For example, EN 16931 defines a business term for the supplier’s name. The standard specifies what that information means and what obligations are associated with it.
However, EN 16931 does not itself prescribe how that information should be technically structured in XML.
Syntax bindings exist for that purpose.
The European standard recognizes two XML syntaxes:
UBL 2.1
and
UN/CEFACT CII D16B
As a result, the same business term can technically be represented in two different ways.
Technically, the XML files look quite different. Semantically, however, they can contain exactly the same information.
3. Why do two standards coexist?
At first glance, it seems inefficient to support two different XML syntaxes for electronic invoices.
In practice, however, UBL and CII stem from different standardization traditions.
UBL was developed as a broad library for electronic business documents. In addition to invoices, UBL also includes structures for orders, order confirmations, shipments, and other commercial messages.
CII stems from the broader UN/CEFACT model for international trade and supply chain communication.
The underlying concept is strongly based on reusable business components that can be applied in various trade processes.
Both approaches can represent the same core invoice.
For this reason, the European standard has not mandated a single syntax but has selected two existing international standards capable of supporting the semantic model of EN 16931.
For organizations, this means that the choice is often not purely technical.
The landscape in which they operate plays an important role.
4. CII plays an important role in Germany
CII is particularly prominent in the German e-invoicing landscape.
Germany supports both UBL 2.1 and UN/CEFACT CII as part of its implementation of EN 16931.
The German standard XRechnung is a Core Invoice Usage Specification under EN 16931. XRechnung can be represented using both the UBL and CII syntaxes.
In addition, there is ZUGFeRD.
ZUGFeRD is a hybrid invoice format that combines a human-readable PDF with a structured XML file. The XML portion is based on UN/CEFACT CII.
The international Franco-German variant of this format is known as Factur-X.
As a result, a single file actually contains two representations of the same invoice:
a PDF for human processing;
and structured CII data for automated processing.
Which CII version is relevant depends on the implementation specification that the document must comply with.
5. A CII invoice is more than just valid XML
Just as with UBL, a technically correct XML file is not automatically a valid electronic invoice.
For example, the XML structure may be built entirely in accordance with CII, yet required information may be missing or a calculation may be incorrect.
That is why there are additional business rules on top of the syntax.
When CII is used within EN 16931, the invoice must comply with the European semantic requirements and the associated validation rules.
These rules specify how the business terms from the semantic model are translated into CII elements.
Additional checks may then be performed.
For example:
- presence of required data;
- correct VAT categories;
- valid currency and country codes;
- correct totals;
- relationships between amounts;
- identification of supplier and customer;
- and specific rules from national implementations.
The value of standardization, therefore, lies not exclusively in XML.
The combination of semantics, syntax, and validation rules ensures that different systems can interpret the same invoice in the same way.
6. CII, XRechnung, and Factur-X are not the same
Because these terms often appear together, CII, XRechnung, and Factur-X are sometimes used as synonyms.
They are not.
UN/CEFACT CII
is the international XML standard used to technically represent invoice data.
EN 16931
describes the semantic European core invoice.
XRechnung
is a German implementation specification of EN 16931. Both UBL and CII can be used for this purpose.
ZUGFeRD / Factur-X
are hybrid invoice formats in which a PDF/A-3 document is combined with structured CII data.
These layers can therefore be superimposed on top of each other.
A Factur-X invoice contains CII. However, not every CII file is automatically a Factur-X invoice.
The same applies to XRechnung.
An XRechnung document can use CII, but it must also comply with the specific rules of XRechnung.
7. CII as Part of a Broader E-Invoicing Landscape
In practice, international organizations are increasingly dealing with multiple e-invoicing standards at the same time.
For example, a Dutch supplier might use UBL via Peppol.
A German customer might require an XRechnung in CII.
Another business partner uses Factur-X.
A sector-specific supplier may use DICO.
In addition, there are ERP-specific XML formats, EDI, API integrations, and PDF invoices.
For the back-end financial system, all these differences are usually undesirable.
Ultimately, the ERP system needs to receive consistent data: supplier, invoice number, invoice date, order reference, amounts, VAT, and payment information.
That’s why an integration layer is important.
A solution like 4CEE Exchange can receive, validate, and—where necessary—convert various channels and formats before the data is forwarded to the financial system.
For example, a CII invoice can be converted to an internal ERP format. A UBL invoice can be converted to the same format.
Conversely, an outgoing invoice can be translated into the standard required by the recipient or local regulations.
The value, therefore, lies not only in supporting CII or UBL individually.
It’s about being able to navigate a landscape where different standards coexist.
UN/CEFACT CII plays a special role in this regard.
Together with UBL, it forms one of the two official XML syntaxes with which the European core invoice from EN 16931 can be represented. At the same time, CII forms the basis for important applications such as XRechnung and Factur-X.
As a result, CII may be less visible than some formats built on top of it, but beneath the surface, it is a key building block of European electronic invoicing.