Re: [ubl] Proposed addition to 2.1 documented constraints - no schema location hints

[Stephen Green <stephen.green@documentengineeringservices.com>]

Just reading Roberto's comments and I think I
agree but would go further: the implementations
of XML are really responsible for ensuring they
can handle the essentials of modern XML
technology like schemaLocation and multiple
prefixes and namespaces. If we made allowances
for difficulties with schemaLocation then it looks
odd because we do not make allowances for
much more troublesome features like multiple
namespaces and prefixes and imported modular
schema files. Even the rule Ken mentioned about
not having empty content is a problem for many
implementations, as I've mentioned before,
because it is notoriously difficult to ensure that
output does not inlcude any empty content and
removing optional elements with empty content
(whilst not removing empty but mandatory elements
and then throwing early enough exceptions for
any empty mandatory elements in time to do
something sensible about it) - all this already is
difficult to implement. So if we don't want to make
these things easy to implement (though I really do)
then why worry about what is a core feature of XML?
The use of schemaLocation is pretty much the usual
use of XML whereas requiring the prevention of empty
elements is, I think, rather an obscure use of XML.

Best regards
---
Stephen D Green




2009/10/15 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
>
> --
> Upcoming: hands-on code list, UBL, XSLT, XQuery and XSL-FO classes
> in Copenhagen Denmark and Washington DC USA, October/November 2009
> Interested in other classes?  http://www.CraneSoftwrights.com/o/i/
> Crane Softwrights Ltd.          http://www.CraneSoftwrights.com/o/
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> Video lesson:    http://www.youtube.com/watch?v=PrNjJCh7Ppg&fmt=18
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> G. Ken Holman                 mailto:gkholman@CraneSoftwrights.com
> Male Cancer Awareness Nov'07  http://www.CraneSoftwrights.com/o/bc
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>
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