Re: [xml-dev] Does the XML syntax have an underlying data model?

[Jim Melton <jim.melton@oracle.com>]

Yes, Rick, I agree with what you said below.

In my mind, you identified precisely the reason why a well-considered 
and -defined data model is important: a data model should fully and 
accurately decode the data used by the applications.  If it does not (or 
there is no data model), then it's much harder to be sure that everybody 
who needs to know the data does -- and that they "know" it in the same way.

That's good for small application systems, but vital for large, 
enterprise-class application systems.

In the case you cited, it seems that the applications needed a bit of 
information (whether an attribute value was defaulted or not) that the 
data model selected/designed did not capture.  Obviously, the people who 
designed the Infoset and the PSVI did not need that information for 
their purposes, and the models don't contain that information...same 
with the XQuery Data Model.  But we could have included that 
information.  And, given a strong enough case, it's not too late.

Jim

On 4/16/2016 11:01 PM, Rick Jelliffe wrote:
> To throw a practical problem in: imagine a global company not unlike 
> where I work: one persistant problem we oops they have with their XML 
> systems, but not with their SGML systems, is that some of their legacy 
> DTDs ported from SGML specify large numbers of default attributes 
> (sometimes 20 default attributes per element), and their documents, 
> which can be large anyway, can multiply in size with useless attributes.
>
> When using Omnimark, we have no problem, because the infoset it 
> operates on includes information on whether a value was defaulted or 
> not. So doing null transformations on documents is possible. With eg 
> Xslt, there is no way to know. So you have to fake it by coding the 
> ATTLIST default rules into xslt to strip out the values. Fragile and 
> bothersome.
>
> Now would having a data model have fixed this? Probably not: the 
> Infoset decided that defaulting was not interesting information and 
> any data nodel built on that would make the same decision. 
> Transformation tools have been built on a data model that is one step 
> removed from the actual XML, but it has meant that one major 
> optimization does not flow through the pipeline.
>
> I dont see that a data model would help move the technology in a 
> direction that would be more optimized for large numbers of default 
> attributes. If you make things, let them solve real problems.
>
> Cheers
> Rick
--
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Jim Melton --- Editor of ISO/IEC 9075-* (SQL)     Phone: +1.801.942.0144
  Chair, ISO/IEC JTC1/SC32 and W3C XML Query WG    Fax : +1.801.942.3345
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