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   Re: [xml-dev] XML Data Modellling/Linking (was RE: [xml-dev] AfterXQuery

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Michael Champion wrote:
> On Fri, 22 Oct 2004 21:15:54 GMT, rpbourret@rpbourret.com
> <rpbourret@rpbourret.com> wrote:
>>Michael Kay wrote:
>>> Why can't we have multiple hierarchic views of the same network?
>>> Why do all my queries have to change depending on whether my footnotes are
>>> inline, out-of-line referenced by IDREFs, or in external documents
>>> referenced by URI? What happened to the old doctrine of data
 >>> independence?
> >
>>Hmmm... Sounds like the relational model. (Sorry, couldn't resist.)
>>I think this could actually be dealt with at the query language level,
> I hope you're not joking :-)
> The CODASYL data model ultimately foundered because of its unwieldy
> links, and XLink foundered trying to do something similar for XML. 
> Maybe the lesson here is that the relational model approach of
> defining links *dynamically* based on relationships on the *values* of
> information items rather than predefined links really is the way to do
> what XLink tried to do.

Agreed, but it's also part of the catch.

Operators that automatically knew to follow links would have to know 
that links are in fact links. And since it is unlikely that the values 
being used to make the link are URIs, they would also need some sort of 
information about the link target.

For example, given the element <part>123</part>, it would be nice to 
link this with a document containing more information about part 123, 
but XQuery would need to know where to go looking for that document.

One possibility is some sort of external document containing link 
information, as Dave Pawson suggests. Note that this could be in the 
form of schema annotations, as this is the normal source of such 
information for XQuery. [Insert groans from the 
I-don't-like-mixing-schemas-and-queries crowd here.]

While schemas might be a good place to tell the query that an element or 
attribute represents a link, I don't think it's a good place to put 
information about where to go to resolve the link, as the schema is 
portable but location information, such as where a parts document is, is 

The other obvious source of the information is the query itself, but 
then we've already got this :)

On a related point, I think it would be nice to be able to just say, 
"This is a link," without any of the additional explanatory information 
that XLink gives (type, role, etc.). The advantage of this is 
simplicity, and it really isn't that unreasonable when you think about 
it: Most interpretation of XML documents is application specific anyway, 
so why should links be any different?

-- Ron


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