Proposed addition to 2.1 documented constraints - no schema location hints

["G. Ken Holman" <gkholman@CraneSoftwrights.com>]

Hi folks,

I'm preparing my training material for next week and something came 
to mind that I would like to consider for inclusion in UBL 2.1 along 
the lines of the additional document constraints.

For example, we have in the additional document constraints section 
6.3 that no UBL element can be empty.  There are two others.

I would like to add a new document constraint that schema location 
hints not be included in UBL documents, thus deprecating 
xsi:schemaLocation along the lines of:

  <Invoice
   xmlns:cbc="urn:oasis:names:...:CommonBasicComponents-2"
   xmlns:cac="urn:oasis:names:...:CommonAggregateComponents-2"
   xmlns="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
   xsi:schemaLocation="
      urn:oasis:names:specification:ubl:schema:xsd:Invoice-2
      u:/cd/artefacts/os-UBL-2.0/xsd/maindoc/UBL-Invoice-2.0.xsd
   ">
   .....

Schema location hints are very platform and user specific.  Including 
such in an instance to a trading partner isn't invalid but could mess 
up that trading partner's processes that take advantage of such hints 
when available.  If their platform obliges them to edit out the 
attribute, then they are not dealing with untouched input instances.

Per W3C Schema 2.6 all schema processors have this declaration 
built-in and thus the current UBL document constraint 6.1 is not 
violated when this attribute is present.

But this introduces a new category of "additional document 
constraints" called something like "recommended additional document 
constraints" or "interoperability document constraints" because it 
cannot be mandated since it was not a rule for UBL 2.0.  Thus UBL 2.0 
instances may have it and we can't say in UBL 2.1 that a UBL 2.0 
instance is invalid.

This isn't something we can say in the schemas, since a W3C Schema 
processor has these attributes built in.

Having chosen the W3C Schema syntax to express the semantics of the 
document constraints has brought this in along as baggage ... if one 
were to create, say, a RELAX-NG model of the UBL schemas, that model 
would necessarily need to include in it a declaration of an optional 
xsi:schemaLocation to accommodate that it is implicitly allowed by 
our choice of schema expression.

Therefore, I think we need a new section in the UBL documentation 
titled along the lines of "Interoperability Document Constraints" 
that documents recommended rules such as this that cannot be mandated 
(due to backward compatibility) but will improve interoperability 
between trading partners from UBL 2.1 and on.

I'm curious to hear your thoughts on this.

. . . . . . . . . . Ken

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