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   Re: [xml-dev] Making a silk purse out of the schema sows ear - was [xml-

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In Schematron - however going for xslt implementation of schematron by
using the current function:

<sch:rule context="table/column[1]">
    <sch:report
test="following-sibling::column[count(cell)&gt;current()[count(cell)]]"
    >cells need to be the same number per column
</sch:report>

</sch:rule>

Cheers,
Bryan Rasmussen




On 2/9/06, Philippe Poulard <Philippe.Poulard@sophia.inria.fr> wrote:
> hi,
>
> IMHO, the main difficulty that schema technologies encounter is their
> poor capabilities to express constraints because they are hard-coded in
> the schema. This is the case for occurrence constraints and content
> model definitions.
>
> I have experimented a schema language that allows to compute the
> occurrence constraints dynamically and that allows to switch from a
> declarative language to an imperative one, which increases dramatically
> the expressiveness of the schema. The idea is to push back the limits of
> the declarative language when they are reached.
>
> An example :
> a RelaxNG user was complaining about a constraint that he couldn't
> express : he had to design a <table> with any <column>s but <column>s
> should have the same number of <cell>s
>
> I respond that he could consider an alternative schema technology, such
> as these that I designed :
> <asl:element name="column">
>    <asl:sequence>
>      <xcl:if test="{ asl:element()/preceding-sibling::column }">
>        <xcl:then>
>          <asl:element ref-elem="cell" min-occurs="{
>   $asl:max-occurs }" max-occurs="{ count( asl:element()/../column[1]/cell
>   ) }"/>
>        </xcl:then>
>        <xcl:else>
>          <asl:element ref-elem="cell" min-occurs="1"
>   max-occurs="unbounded"/>
>        </xcl:else>
>      </xcl:if>
>    </asl:sequence>
> </asl:element>
> The full schema and the running results are available here :
> http://groups.google.com/group/comp.text.xml/browse_thread/thread/d97cd4adf1964fdb/2f92e65b7ad48dff?hl=en#2f92e65b7ad48dff
>
> This demonstrates that a simple if-then-else statement allows to build a
> made-to-measure content model with dynamic occurrence constraints.
>
> I named that schema language the Active Schema Language and I have an
> almost full implementation of it in Java, called RefleX :
> http://disc.inria.fr/perso/philippe.poulard/xml/active-tags/active-schema/active-schema.html
> http://reflex.gforge.inria.fr/
> You can read the examples, download the tool and play with it.
>
> Moreover, ASL allows to design smart data types ; there is a tutorial in
> the RefleX web site that shows a semantic data type : the "temperature"
> data type, which is able to parse "32F" and "20C" ; as this type is
> used to augment the amount of information of the XML document, we can
> sort a list of attributes of this type not on the string values but on
> the typed values
> http://reflex.gforge.inria.fr/tutorial.html#N800F69
>
> It is worth seeing because all the problems you consider in your message
> are pointed out and solutioned in ASL.
>
> Michael Champion wrote:
> > I think the reality is that lots of people flipped the Bozo Bit on the
> > XSD spec in 1999-2000.  They went in different directions, however:
> > Some to alternative schema languages, some to radical simplification of
> > XML to de-emphasize schemas altogether.
> >
> >
> >
> > In hindsight, had  people foreseen today's reality that we're stuck with
> > XSD as what the mainstream user thinks of as the "real standard",
> > clearly the energy would have been better spent debugging the wretched
> > thing rather than trying to pretend it doesn't exist or trying to drive
> > a stake thru its heart.  I'm more interested in discussing what to do
> > going forward given the current mess.  The problems I see are:
> >
> >
> >
> > - The W3C is more interested in moving the XSD spec forward than fixing
> > its numerous ambiguities.  (Their pushback is that the people who want
> > to fix it are not represented on the WG, and the people who have skin in
> > the game want to move forward).
> >
> > - RELAX NG is clearly "better" for textual documents but doesn't have
> > much support for the data-oriented use cases. (Sure you can plug in the
> > XSD type system, but that's a big part of the problem).  We now have an
> > unpleasant situation of fragmentation where there's little mainstream
> > tool support for RELAX NG due to lack of demand, exploitation of its
> > geek chic (partly to strike a blow against the empire, I suppose), with
> > the result that the normative definitions of Atom and ODF can't be used
> > with most commercial XML tools.  Maybe a good guerilla tactic in the
> > open source wars, but for the moment it's the innocent who suffer the
> > collateral damage.
> >
> >
> >
> > - Schematron is moving forward as an ISO standard and has some good
> > implementations but has few normative references in vertical industry
> > standards nor mindshare.  (Correct me if I'm wrong about the normative
> > references).
> >
> >
> >
> > - Lots of people complain about the limitations of XSD that Schematron
> > addresses and the W3C doesn't plan to, especially the lack of occurrence
> > constraints.
> >
> > The best way forward that I can see is to encourage end users to
> > employ XSD + Schematron as necessary, and encourage W3C to address XSD's
> >  bugs and ambiguities before adding more onto an unstable foundation.
> > What does that miss that the world actually values? (as much as it
> > depresses me to say it, the world doesn't seem to value RELAX NG's
> > elegance and mathematical foundation very much).
> >
>
> --
> Cordialement,
>
>                ///
>               (. .)
>   --------ooO--(_)--Ooo--------
> |      Philippe Poulard       |
>   -----------------------------
>   http://reflex.gforge.inria.fr/
>         Have the RefleX !
>
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