Invoice: Validating summary data

[Isak Hansen <isak.hansen@gmail.com>]

I've been tasked with maintaining a mediator-of-sorts for UBL
invoices. We've been using it internally for a while, but are having
issues after opening up for external systems which are sending us
'broken' data. One example of this was an ignored-in-calculations
invoice line containing the grand total for that invoice.

We currently only validate documents against the schema, verify that a
customer and supplier id is present, and that (supplier, invoice
number) is unique. I know there's a lot of UBL-validation-tools out
there, and wonder if any of these do sanity checks on the
LegalMonetaryTotal and TaxTotal elements.

If not, what are the absolute minimum of fields we should be checking
before accepting an invoice (for relaying), just as a guideline? If
someone could point me towards a resource for all the calculations I
should be doing, that would be appreciated as well.


Thank you,
Isak