Re: [ubl-dev] Re: Global elements doing UBL a disservice

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

At 2006-05-22 07:53 +0800, Chin Chee-Kai wrote:
>Hi, I think Stephen had given me some help on understanding more
>about the extensibility discussed in Joseph Chiusano's example,
>that it was more on the simple type extensions and restrictions,
>and so impacts on how CCTS was to be implemented and observed
>at the same time, versus the extension points that are to be
>sited within complex types that you've keenly worked on (or
>are keenly working on).   So perhaps there's no conflict in what
>we're talking about.

I hope there is no problem.  I confess a difficulty in understanding 
the issues related to CCTS.  I thought it was a model and not a 
syntax, and that the CEFACT XML NDRs translated the model into XML 
syntax.  But I don't understand how that relates to UBL as a problem 
issue if UBL has its own NDRs to translate the model into XML 
syntax.  Provided the model is the same, then there exists a 
well-defined mapping between the two instantiations.

And I'm assuming the UBL NDR's preserve the model, so it doesn't 
matter if it is different syntax than CCTS.

But I could very well be wrong, and hope that someone better informed 
than I can clarify this.

>Help me understand here, but I didn't see how the discussions of
>Stephen and Joseph and others like David, Fraser, Fulton and perhaps
>others I've not mentioned, had concluded beyond reasonable doubts
>(sorry, watching too much of Boston Legal... :)  that it is clear
>that W3C Schema features are not sufficient to the task, as you've
>put it.   It's not so clear to me at least.  How did the conclusion
>get drawn?  What exactly was the requirement and in what way is W3C
>schema inferior to meeting that requirement?

Because all of the W3C mechanisms described up until that point, and 
the ones discovered last week in Belgium end up not being able to 
describe subsets and supersets of the UBL information set precisely 
nor completely.

Three examples that I am putting into a white-paper I am writing on 
this for discussion by the TC:

(1) - if a subset wishes to elide an optional information item, I 
believe there is no way to set the cardinality of a construct to zero 
in a redefine, but this might not be a problem since I'm confused 
about the features and limitations of redefine

(2) - if substitution groups or W3C extension techniques quoted add a 
new information item to an existing information item, and this is not 
done in the extension area, then instances of the extended document 
are not validated against the base (which is, I believe, the basis of 
global interoperability) which has the same namespace URI string

(3) - the extension area cannot be declared as having "all but a set 
of namespaces" for namespace-qualified children, only "all" or "all 
others but this one", which is insufficient (and I was told what I 
need cannot be done by W3C Schema experts in XML-Dev and W3C-Schema mail lists)

For example, in RELAX-NG I can say:

element UBLExtension =
  {
   element * - ( in:* | cbc:* | cac:* ) { ...........

This would allow the extension point to have anything outside of 
UBL-defined namespaces.  This is not possible in W3C Schema speak.

In my paper I'm proposing using the SBS method of describing subsets 
which can be used to synthesize constraint expressions that people 
may wish to use.  Those who want to use RELAX-NG can use it.  Those 
who want to use W3C Schema can use it, but will have problems unless 
they layer NVDL on top or a very extensive Schematron expression that 
may be unwieldy.

>It would be a rather surprising conclusion to draw, that UBL
>requirements are so high that W3C Schema cannot meet the kinds
>of requirements to describe the desired data sets.

Or that W3C Schema semantics are so low that necessary markup 
patterns needed to meet real-world requirements cannot be expressed 
by the limitations of the language.  The RELAX-NG schema language has 
sufficient semantics for the patterns that are needed.  W3C Schema 
was developed for program-to-program exchange of inherited type 
information ... it is not sufficiently flexible for the kinds of 
markup patterns that we need.

>If so, what more
>would be needed of the expenses on getting the right software, testing
>for the correct implementation, and the bottom line, allowing more
>people (including SMEs) to use UBL?

That depends ... if they use pure W3C Schema and pure W3C Schema is 
not up to the task, and reducing UBL to satisfy W3C Schema to the 
point of causing real-world problems in interchange, then they'll 
have to take the risks.

>Of course, if we design UBL
>schemas in a way that requires precisely what W3C schema cannot
>possibly offer, the question, if we allow for simplicity and
>compactness, then becomes, can the same set of data instances
>desired by UBL be described with only those facilities offered
>by W3C schema?

Apparently not ... the experts have told me I cannot do what I want 
to do.  I've heard the clamour for a pure W3C-Schema approach and I 
have been agonizingly trying to find just a way to do that, for fear 
of being branded a zealot for pushing unnecessary technologies.

>Anyway, back to the thread's subject, it would also seem that for
>the xsd:any mechanism you're developing, the same mechanism could
>go under global or local type declarations.

I'll let you assess that ... as I am a fan of global declarations for 
all elements and types (as it makes management easier), I have not 
determined drawbacks in this approach.

>I certainly hope we're not at the juncture of seeing the emergence
>of requirements for other additional data description languages in
>UBL 2.0.  That might be too fast, too soon....

"Additional yet to be conceived data description languages"?  No ... 
there are existing ISO data description languages that work just fine 
... it just happens that W3C Schema expression semantics aren't 
powerful enough for straight-forward means.  It would be unfortunate 
to compromise the data integrity to fit a tool, rather than find the 
right tool to fit the data integrity.

I'm hoping to soon summarize my ideas so that I can get the opinions 
of the committee.

If the committee decides to loosen up the integrity to allow a pure 
W3C Schema expression of the constraints, then the integrity checking 
moves to user guidelines instead of formal expressions.

I'll teach whatever the committee decides ... but while it is 
deciding I will present opportunities that are available.

Thanks for your patience, Chee-Kai, for me to answer your question.

. . . . . . . . . Ken

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