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   Re: RE: [xml-dev] XQuery and DTD/Schema?

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At 02:54 PM 7/6/2002 -0400, Simon St.Laurent wrote:
>At 02:30 PM 7/6/2002 -0400, Jonathan Robie wrote:
>>For data that is physically represented as XML, there already *is* a 
>>layering - XML text is parsed to create an Infoset, which is validated to 
>>create a PSVI, which is mapped into the XML Query data model. Do you 
>>suggest a different layering? What layering would you prefer, and how 
>>would this relate to the XML Query data model and typed operatoins?
>That's easy.  Layer XML Query on the Infoset, drop the PSVI, and you have 
>half a chance of producing something likely to have a long and useful lifetime.

That's not layering, that's deciding that data is not typed unless I 
require explicit casts, convert it to Java or relational data, or whatever. 
And that makes many simple examples come out wrong, eg:

   let $x := <foo xsi:type="decimal">39.42</foo>
   let $y := <foo xsi:type="decimal>147.23</foo>
         if ($x < $y)
              then "x is less"
              else "y is less"

Your approach would mean that the above query would return "y is less". 
Trust me, many users of XQuery would not like that.

>Otherwise, change the name to PSVI Query and let us XML folks get on to XML.

XQuery and XPath have created a simple, typed data model for XML - I think 
this is a Really Good Thing [1]. XQuery is defined in terms of this data 
model, not in terms of the PSVI, which was created for different purposes 
and is really on the wrong level of abstraction. There is a mapping to this 
data model from the PSVI, and mappings in the works for at least DTDs, 
well-formed XML, and XML views of relational data.


[1] http://www.w3.org/TR/query-datamodel/


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