Real-world e-invoicing¶

The earlier sections teach the XML technologies one at a time: XSD for structure, Schematron for business rules, XPath and XSLT underneath both. This section is where they meet a real problem — European electronic invoicing — and stop being abstract.

Almost every example in this site has quietly used the same domain: a UBL invoice, the EN16931 rule BR-01, a currency code. That is not a coincidence. E-invoicing is the canonical modern XML application: a public semantic standard, two XML syntaxes, a layered validation stack, and shared code lists — exactly the four technologies this site covers, assembled into one pipeline.

The cast¶

How the layers stack¶

A document is not "valid" or "invalid" against a single thing — it passes through a stack, and each layer catches what the layer below cannot.

flowchart TD
  I["UBL / CII instance"] --> X["XSD<br/>structure & datatypes"]
  X --> E["EN16931 Schematron<br/>BR-* business rules"]
  E --> P["Peppol Schematron<br/>profile rules"]
  P --> C["Code-list checks<br/>(Genericode)"]
  C --> OK["Accepted"]

The pages¶

1. Anatomy of a UBL invoice — walk a small invoice: namespaces, cbc/cac, and how EN16931's BT-/BG- business terms map onto the XML.
2. A UBL invoice in detail — the full OASIS example taken apart block by block, with the totals reconciled by hand.
3. The validation pipeline — XSD, then EN16931 Schematron, then profile and code-list checks: what each layer is for.
4. Genericode code lists — the .gc format, and looking codes up efficiently with xsl:key or a map.
5. Peppol and CIUS profiles — how EN16931 is specialised for real networks, and why a profile may only narrow, never loosen.
6. The Peppol network — the four-corner model, Access Points, SML/SMP discovery, and AS4: how an invoice is actually delivered.