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Re: Access to Schema API information

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Tue, 18 Sep 2012 10:26:34 +0100
To: Michael Kay <mike@saxonica.com>
Cc: "w3c-xsl-query\@w3.org" <w3c-xsl-query@w3.org>, "xmlschema-dev\@w3.org" <xmlschema-dev@w3.org>
Message-ID: <f5bd31jznp1.fsf@calexico.inf.ed.ac.uk>
Michael Kay writes:

> On 22/05/2012 11:06, Henry S. Thompson wrote:
>> Michael Kay writes:
>>
>>> I have been implementing a Saxon extension that exposes the Schema
>>> Component Model to XSLT and XQuery applications
>> Using functions is cool, but did you consider sticking with XPath?
> It does stick with XPath, only it's XPath 3.0...
>
> I think that attempts to model this information using elements and
> attributes suffer two main problems:
>
> (a) the node identity problem. It's hard to get away from the fact
> that elements have identity, and if elements have identity and model
> schema components then there is a strong expectation that node
> identity reflects component identity, which (a) doesn't reflect the
> semantics of the model (which explicitly leaves identity undefined),
> and (b) makes a lazy implementation difficult.
>
> (b) the network modelling problem: the schema component model is a
> network, while XML is best at modelling trees. Any attempt to model a
> graph in XML leads to (a) to arbitrary decisions about which
> relationships to model as XML parent/child relationships, and (b) very
> clumsy navigation when you have to follow the non-hierarchic links.
>
> Using a functional model of the information neatly bypasses both these
> issues. Functions in the XPath 3.0 model have no identity, so there is
> no way of asking, for example whether two facets with the same
> properties are "the same facet". All navigation is done using function
> calls so there is no asymmetry between relationships "within the
> hierarchy" and relationships "across the hierarchy".
>
> Michael Kay
> Saxonica
>>
>> See an old Extreme paper for some work we did in Edinburgh along those
>> lines a long time back now:
>>
>>    Uniform access to infosets via reflection
>>    Extreme Markup Languages 2003
>>    http://www.ltg.ed.ac.uk/~ht/Extreme_2003.html
>>
>> ht
>
>

-- 
       Henry S. Thompson, School of Informatics, University of Edinburgh
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
                       URL: http://www.ltg.ed.ac.uk/~ht/
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Received on Tuesday, 18 September 2012 09:27:12 GMT

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