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At 09:53 20/06/2006, Rick Jelliffe wrote:
>There are indeed many useful kinds of schema languages that don't
>have widespread currency yet.
Many thanks Rick
This is very useful - if nothing else it reassures me I am on a
reasonable track.
>In some of my company's products we use our own little schema
>language that says
>
>* what elements are allowed or required
>* what attributes are allowed or required
>* what elements are only every found in first or last position
Yes..
>We also have "usage schemas" which sample documents and generate all
>the possible grandparent/parent/child paths in the document, and
>checks other documents against these.
>
>Checking lists of tokens is indeed a very problematic area for
>Schematron using the default XSLT 1 implementations.
Agreed.
>ISO DSDL was created to give a home and official status to these
>kind of little languages. If anyone can come up with a technically
>excellent and implemented little schema language that helps validate
>some significant kinds of markup idioms that XSD or the other ISO
>DSDL schema languages do not cover well (as is *entirely* possible),
>I am certain the ISO SC34 WG1 group would be interested in
>considering it for standardization.
I am not a great fan of developing things through ISO - I have sat on
ISO ctte and the speed is extremely slow. I am less concerned about
post-acceptance. But I am actually hoping that there are others who
are interested in doing this as well.
>To be honest, I suspect that Schematron with a particular extension
>could pretty much do what Peter requires. In particular, ISO
>Schematron has a macro facility called abstract patterns that allow
>you to be much more declarative in labelling the participants in a
>schema relationship: you could have one like
Good. This may be useful to pursue. If it is lightweight and useful I
would be prepared to write my own implementation.
><sch:pattern name="required-child" abstract="true">
> <sch:rule context="$parent">
> <sch:assert test="$child">The parent should have a child</sch:assert>
> </sch:rule>
></sch:pattern>
$foo seems to be an argument of some sort
> <sch:pattern name="eg" is-a="required-child">
> <sch:param name="parent" value="Angela"/>
> <sch:param name="child" value="Suhai"/>
> <sch:param name="position" value="1" />
> </sch:pattern>
>
>What this gives is enough markup that a custom processor can take
>the schema and
>generate code based on it. For example, to append a Suhai element
>to the Angela
>element in the first position.
Yes
>Abstract patterns represent, I hope, a significant advance in
>home-made schema languages, because not only do you get the
>background boring power of XPath validation, but you also get the
>extra labelling required to enable identification of the parts of
>constraints and assertion
>tests. And that identification opens the door for re-targetting the
>schema for purposes such as code generation or any kind of useful
>purpose. XPaths are great because they are terse; abstract patterns
>overcome the concomitant lack of declative expressiveness.
Absolutely agreed. I think the main problem is simply enough courage
to pursue this.
P.
>Cheers
>Rick
>
>
>
>
>Peter Murray-Rust
>Unilever Centre for Molecular Sciences Informatics
>University of Cambridge,
>Lensfield Road, Cambridge CB2 1EW, UK
>+44-1223-763069
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