Hello,

 I am researching information on UBL to introduce it in my organisation.

 I noticed that the InvoiceType can contain one-or-many InvoiceLine which are associated with an Item.

In my organisation, invoices contain invoice lines too. However, invoice lines are grouped by their item category. The category name is a subheader before each invoice line group whose items are part of the same category. Categories are like "Services", "Software licences", "Subscriptions", "Network hardware", "Server hardware", etc.

Example:

 Subscriptions
-----------------------------------------------------------------------------------
* Invoice Line 1 - Item: yearly subscription ABC $100
* Invoice Line 2 - Item: yearly subscription XYZ $50

---> Subscriptions subtotal = $150 

Software licences
-----------------------------------------------------------------------------------
* Invoice Line 3 - Item: 50 seats licence for software A $50
* Invoice Line 4 - Item: 4 CPU licence for software B $10

---> Software licences subtotal = $60

How would you define these categories?

Would it be an InvoiceLine and each invoice line would be in SubInvoiceLine?

Would it be defined in the InvoiceLine Item in one of the various *ItemIdentification ?

Should we extend the InvoiceLineType so they can be grouped by a category ?