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   AFs and linking (was Weak DTDs)

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  • From: Richard Light <richard@light.demon.co.uk>
  • To: xml-dev@ic.ac.uk
  • Date: Mon, 20 Oct 1997 09:39:10 +0100

In message <199710181343.JAA21462@exocomp.techno.com>, Peter Newcomb
<peter@techno.com> writes
>It is true that there is nothing "meta" about meta-DTDs.  They should
>be called architectural DTDs instead, where "architectural" means
>"used via the SGML architecture mechanism defined in Annex A.3 of
>ISO/IEC 10744:1997", or "designed to be used architecturally", as in
>the case of the HyTime architecture's DTD.  Architectural DTDs are
>just DTDs being used in a different way.
>And yes, architectural processing _is_ tantamount to parsing with
>respect to an alternative schema, only the architectural schema is
>better protected from the individual needs of documents, and
>individual documents are better protected from the generalized needs
>of the architectural schema.

Does this mean that architectural processing can be used to deal with an
issue that was raised some time ago, echoes of which I can see in the
current discussion?  That is the ability to pull in 'foreign' documents
(or parts of documents) using XLL, and to then treat them, temporarily,
as though they were part of the current document.

This would be using the architectural DTD like a relational View - "a
virtual table that does not really exist ... but looks to the user as if
it did".

To take an example from my own area of interest (museum information), I
want to store information about objects, people, places, events, etc. in
separate documents to avoid redundancy.  Instead of repeating a few
(randomly-)selected details about a person each time they are mentioned
in an object record, I will just provide an XLL link to their full
biographical record:

<production>Made by <person linktarget="biographies.xml#a00324">
</person> <date>between 1925 and 1927</date> ...

However, this means that I then need a mechanism to traverse the link
and pull in some information from the bio record - the person's name
would be a good start!  What I want is to be able to treat the
PRODUCTION element (on this occasion) as though it contained a PERSON
element populated with information from the bio:

<production>Made by <person><name>Ernest Jones</name><dates><birth>1896<
/birth></dates></person> <date>between 1925 and 1927</date> ...

On other occasions I might want more (or different) information from the
linked biographical document.  This could be achieved by employing a
different architectural DTD.

I'm sure (?) that this selection of elements from linked documents can
be done with XSL, but having support for 'views' would:

- separate out structural issues ('transformation') from presentation
issues ('style');
- simplify the resultant XSL specs;
- offer the client more flexibility over what they did with the
resulting virtual document, since it would still be an XML document
rather than an XSL output.

Any thoughts, anyone?

Richard Light.

Richard Light
SGML/XML and Museum Information Consultancy

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