Missing Date Format Validation (YYYY-MM-DD) in EN16931 UBL Schematron

[AndreasSchmitz1]

The EN16931 UBL Schematron currently does not validate the format of date fields (e.g. cbc:DueDate, cbc:IssueDate). As a result, invoices containing incorrectly formatted dates such as 22018-04-13 pass validation but cause downstream errors in visualization tools (e.g. KoSIT XRechnung viewer). The CII Schematron already includes a corresponding rule (CII-DT-097) for date format validation, so this issue requests the addition of an equivalent rule for UBL to ensure consistent validation behavior across both syntaxes.

[MartinForsberg-Ecru]

UBL XSDs checks for date formats. The schematron rules assume/requires that XSD validation has been passed and many rules can fail catastrophically if the instance isn't XSD valid. This goes for both UBL and CII.

[bdewein]

XSD validation passes for calendar year representations of four to nine digits. So, e.g. <cbc:DueDate>2233422018-04-13</cbc:DueDate> will pass xsd validation. The ISO 8601 norm defines the representation of calendar years by four digits, unless specified otherwise. For CII, however, a restriction is set to maximum four digits (CII-DT-097). Same should apply to UBL.

[MartinForsberg-Ecru]

Thanks, I stand corrected :). I was quick and responded assuming it was about non-valid dates. Since the EN16931-1 says "Dates shall be in accordance to the “Calendar date complete representation” as specified by ISO 8601" I agree that a schematron rule should be added to validate this.

[DougHillERST]

Hi all I think PEPPOL has a rule that checks this https://docs.peppol.eu/poacc/billing/3.0/2025-Q2/rules/ubl-peppol/PEPPOL-EN16931-F001/

[wimkok]

ISO 8601 prescribes, as a minimum, a four-digit year [YYYY]. But: To represent years before 0000 or after 9999, the standard also permits the expansion of the year representation but only by prior agreement between the sender and the receiver. To allow this type of agreement xs:Date allows year longer then 4 numbers. xs:Date used in the xsd for validation allows a year longer than [YYYY]

But i think we must follow common sense for business documents and do the validation in a business rule like the one used by PEPPOL.