Rule at a Glance
| ID | Severity | Context (XPath) |
|---|---|---|
| Series ref. BR-68 | Fatal (error) | cac:InvoiceLine/cac:InvoicePeriod | cac:CreditNoteLine/cac:InvoicePeriod |
| Schematron ID: ibr-085 | Field: ibt-134 — Invoice line period start date, within ibg-14 | ||
Classification
Contextual — the rule constrains one date against another date in the same document rather than against a code list or a format.
What the Rule Is Checking
Where an invoice line declares its own billing period, that period's start date must fall on or after the start date of the document-level invoice period. The test passes if either date is absent, so a line period is permitted where the document has none, and a document period is permitted where lines have none.
The comparison is a date comparison rather than a string comparison — the schematron casts to xs:date before comparing.
Why This Rule Exists
Billing periods drive the tax point on continuous supplies. A telecoms invoice, a maintenance contract, a lease, a subscription: each is invoiced for a period, and the period determines which return the output tax belongs in. Where line-level periods contradict the document-level period, the invoice makes two incompatible statements about when the supply happened.
For an authority operating a real-time regime the invoice period is the primary evidence of tax point. A line claiming to cover a month that starts before the document period opens is either a data error or an attempt to pull revenue into a different reporting window, and the validation layer cannot tell which. It rejects both.
The practical exposure sits at period-end. Continuous-supply invoices issued around a quarter boundary are exactly the documents where line periods get manually adjusted, and exactly the ones where this rule will start failing at the point transmission is most time-critical.
Standard / Code List
Not applicable. Dates follow the ISO 8601 YYYY-MM-DD format required across the profile.
UAE Data Example
PASSES ✓: Document period 2027-01-01 to 2027-03-31, with a line period of 2027-02-01 to 2027-02-28 for a service activated mid-quarter.
PASSES ✓: Document period 2027-01-01 to 2027-01-31 with line periods identical to it.
FAILS ✗: Document period 2027-01-01 to 2027-01-31 with a line period starting 2026-12-15, added to bill an arrears item from the prior month without adjusting the document period to cover it.
What Your ERP / IT Team Must Ensure
- Derive the document-level invoice period from the earliest line start and latest line end where lines carry their own periods, rather than defaulting it to the billing run date.
- Block or route for review any billing document where a line period start precedes the header period start, at creation rather than at transmission.
- Handle arrears and catch-up billing by extending the document period or issuing a separate document, rather than leaving an out-of-range line period on the current invoice.
- Test the subscription, lease and contract-billing scenarios specifically. Standard goods invoices carry no period at all and will never exercise this rule.
Related Rules
The companion constraint on the line period end date sits immediately alongside this one in the schematron, and the document-level period rules govern the header dates this rule compares against. A billing engine that gets header period derivation wrong will trip several of them at once.