On Mar 17, 2006, at 8:56 AM, G. Ken Holman wrote:
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:
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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Box 266, Kars, Ontario CANADA K0A-2E0 +1(613)489-0999 (F:-0995)
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