Re: [xml-dev] UBL

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

At 2006-03-16 21:46 -0600, Dave Scott wrote:
>I was curious about opinions and experiences people on the list might
>have regarding the UBL NDR:
>
>-  Am I alone in finding it too be overly draconian?

The "Garden of Eden" approach to UBL declarations have allowed me to 
mechanically analyze the schema expressions using XSLT that I think 
would have otherwise not been possible (thankfully, I didn't have to 
try to do it otherwise).

>-  What practical limitations (particularly processing limitations)
>have you encountered when implementing the standard?

How often is processing impacted by schema constraint expressions?

>Perhaps my biggest problem with the NDR  is the prohibition against
>custom attributes.

I'm not sure what you mean by a "custom" attribute.  If you mean 
attributes from a foreign namespace, then a combination of ISO/IEC 
19757-3 Schematron (to test the presence of the attribute) with 
ISO/IEC 19757-4 NVDL (to test the validity of the attribute and the 
validity of UBL without the attribute), perhaps even (optionally) in 
combination with ISO/IEC 19757-2 RELAX-NG (to express the constraints 
of the attribute) would seem to me to do the trick.

All without needing any blessing or accommodation by the UBL 
committee since this is all totally orthogonal to the UBL schema expressions.

>I'm contributing to a workgroup to develop a data
>standard which will be used to transmit potentially huge data sets.
>Understandably, we'd like the standard to be friendly to stream
>processing.  The ability to add "type" and "role" attributes in key
>places in the schema would greatly aid processing the data in a way
>that would only require examining the current element stack during
>stream processing for our most typical use cases.

Sounds good.

>The UBL proponents
>on the workgroup propose requiring such items to be a first child
>(rather than attribute) of the node they qualify so as to act as a
>processing flag for its siblings and siblings' children.

Yuck ... I would far prefer flagging such as attributes.  Of course 
if the information you need to include is structured you would have 
to use elements.

>Also, I believe you shouldn't  add
>ordering constraints to your schema, burdening both the production
>and validation of the data set, unless there is a semantic
>motivation.

Indeed.

>A couple of key individuals on the workgroup are adamant about
>adhering to the UBL NDR (although not very articulate when it comes
>to justifying either the individual requirements of the NDR or the
>blanket decision to follow it slavishly.)

Fine ... you can (and I believe *should*) leave the UBL schema 
expressions created by the NBR untouched and sacrosanct.  Layer your 
requirements on top of a read-only schema expression using ISO/IEC 
19757 DSDL http://dsdl.org parts.

>Unfortunately, the
>literature I've been able to turn up regarding the UBL NDR all reads
>like marketing literature rather than frank evaluations of the 
>trade- offs the NDR involves. (My best source has been the UBL mail archives
>but it's fragmented and skimpy on this topic.)  Can anyone point me
>to some more thoughtful evaluations of the NDR?  Or, perhaps,
>implementations of CCTS that allow custom attributes?  Or, better
>yet, UBL endorsed mechanisms for integrating custom attributes with
>otherwise UBL NDR compliant schema?

The propositions to use DSDL layered on top of UBL schema expressions 
are only now being considered.  No decisions have been made and no 
recommendations are written down.  You will find a discussion of 
supplementing UBL schema expressions in:

   http://www.oasis-open.org/archives/ubl/200602/msg00117.html

As tools mature and experience using these evolving standards builds, 
I firmly believe we will be seeing wide-spread acceptance of these techniques.

I hope this helps.

. . . . . . . . . . . Ken

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