EN 16931 and ViDA E Invoicing

EN 16931 & ViDA E-Invoicing

This is the one standards mapping in SIGNET that is not just asserted but runnable and continuously proven in CI. The repository ships a reference transform that projects a canonical SIGNET Invoice into UBL 2.1 / Peppol BIS Billing 3.0 (EN 16931 compliant), and a verifier that reconciles the key Business Terms and the monetary totals.

Why this matters: EU ViDA

The EU VAT in the Digital Age (ViDA) package mandates structured, cross-border e-invoicing based on the EN 16931 semantic model (from July 2030), preceded by national B2B mandates. A procurement network that cannot emit an EN 16931-conformant invoice cannot participate.

Because the SIGNET Invoice is mapped field-by-field to EN 16931, a SIGNET network can emit the exact artefact a tax authority or Peppol Access Point expects — without a bespoke integration per jurisdiction.

The EN 16931 alignment

A SIGNET invoice carries 33 EN 16931 Business Terms / Groups (BT-1…BT-158, BG-4/7/23/25). The mapping lives in three places:

• Invoice — header and totals (BT-1, BT-2, BT-3, BT-5, BG-4, BG-7, BT-106/109/110/112/115, BT-9, BT-20, …).
• InvoiceLine — line detail (BG-25: BT-126, BT-129, BT-130, BT-131, BT-146, BT-151, BT-152, BT-153, BT-158).
• VatBreakdown — VAT subtotals (BG-23: BT-116, BT-117, BT-118, BT-119).

Each schema field records its BT/BG reference in a $comment, so traceability is structural, not documentary. (For why $ref fields are wrapped in allOf, see Foundation Layer → InvoiceLine.)

The runnable proof

Two npm scripts demonstrate convertibility end to end:

npm run transform     # projects examples/invoice.json -> examples/invoice.ubl.xml
npm run verify-ubl    # parses the UBL and reconciles every EN 16931 value

Tool	Language	What it does
tools/signet-to-ubl.js	Node (dependency-free)	Projects the canonical Invoice into UBL 2.1 / Peppol BIS Billing 3.0. Each mapping is annotated with its BT/BG reference.
tools/verify-ubl.py	Python	Parses the generated UBL and reconciles every key EN 16931 Business Term and the monetary totals against the source invoice; exits non-zero on mismatch.
examples/invoice.ubl.xml	—	The committed generated output, so the projection is visible without running it.

Both run in CI on every push (see .github/workflows/validate.yml), so "convertible to Peppol BIS" is a continuously-proven claim, not an assertion.

The worked numbers

The worked invoice (examples/invoice.json) is arithmetically self-consistent and reconciles end to end:

Quantity	Value
Line 1 — Core router managed service, 100 × €50/MON	€5,000 net
Line 2 — Field engineering, 10 × €120/DAY	€1,200 net
Line extension / tax-exclusive total	€6,200 net
VAT @ 21% (category S)	€1,302
Tax-inclusive / payable amount	€7,502

€6,200 net + €1,302 VAT @ 21% = €7,502 payable — the verifier confirms each of these survives the projection to UBL.

Scope and limits

The shipped transform is a faithful reference projection, not a substitute for official Peppol validation. Production use should additionally run the output through the official Peppol / EN 16931 XSD + Schematron validation artefacts.

See CHANGELOG 0.3.0 for the full description of the transform and verifier.

Where to go next

• Worked Examples → Invoice.
• Standards Mapping — the full bridge table.
• Validation & Conformance — how CI enforces all of this.