RE: Crazy idea

["Maxime Levesque" <maximel@xxxxxxxxxxxxxx>]

 I like the idea very much, have you tried it on a lot
of examples ?

 Is it hard to generate (automatically) an XSLT
stylesheet for a given XSchema ?

 It's a good oportunity for reuse (of code and architecture)

 It seems that XSLT has more uses other than for what it's
designers had in mind, for example I use it for XML to Object
mapping, I have a big and complex tree of objects, I persist it
by writing it's XML representation in a file, (that's the easy part),
the hard part (from XML to Objects) I use XT, (but any XSLT processor
that can take objects as parameters would do). Of course I only
use XPath and java extensions (I don't produce any result tree),
so a stand alone java implementation of XPath would be just as good.


> Mulling over the namespace/XSchema issue, I came up with the following
> notion. I wonder if it has ever been suggested, and what its chances are.
>
> A DTD/XSchema, as defined today, performs two tasks. One is to validate a
> document. The output of this is a single Boolean value. The other is to
> "complete" the document - that is, add defaults.
>
> The latter part seems like a transformation task to me, which raises the
> question: why not specify this as an XSLT stylesheet? Once you consider
> this, it becomes obvious that the first part can also be specified as a
> stylesheet, given that one introduces some way for a stylesheet
> to indicate
> an error in the input (say, <xsl:error>). Actually, that's a good idea by
> itself. I already simulate it in my stylesheets by emitting an obtrusive
> error boilerplate, but that's a kludge.
>
> Objections:
>
> - You need an XSLT processor instead of just an XSchema processor.
>
> Given that an XML system is likely to have an XSLT processor anyway, this
> might be viewed as removing a component instead of adding one.
>
> - Doing full XSLT processing is more expensive then "just" XSchema
> processing.
>
> Is it? The XSchema spec is already quite complex, what with schemas
> importing one another and so on. There's also the issue that if
> we'd be only
> using XSLT, then the effort that would have gone for writing XSchema
> processors would go instead for optimizing XSLT.
>
> - XSLT is be "too strong". After all, it is Turing complete.
>
> XSchemas are already stronger then DTDs, for a good reason, so
> this might be
> an advantage. Otherwise, it might be useful to define a subset of XSLT to
> use in "schema" stylesheets.
>
> - People would abuse it.
>
> That is, people would create "schema" sheets which would transform the
> document to something completely different then what you started
> with. There
> are several answers to this, ranging from "so what? anything good can be
> abused" to "define a strict subset of XSLT which can't be abused". My
> suggested compromise is to require that a "Schema" XSLT stylesheet should
> only emit "fixpoint" documents - that is, applying it a second
> time must be
> a no-op. This is trivially testable and satisfies most objections
> as to the
> difference between "validation/completion" and "transformation".
>
> - The XSchema WG would be out of job :-)
>
> Someone should consider what modifications, if any, are required for using
> XSLT in this capacity. We'd need <xsl:error> or something equivalent (a
> construct which is useful in general). There might be a need to pick a
> subset of XSLT. There may be other issues. The whole concept of using XSLT
> for validation would justify a separate spec. So the Schema WG would
> actually be quite busy formulating it.
>
> The benefits are obvious:
>
> - KISS.
>
> Just one spec, instead of two; just one implementation, instead of two. In
> fact, I'd consider this an overriding consideration. The burden of proof
> should be on the other side to justify the need for a separate spec :-)
>
> - Time to recommendation.
>
> The recommendation could be released very soon after the XSLT one. That
> should be much faster then the current expected time for XSchema
> to finalize
> (I think). This can be done since A lot of sticky issues in the
> XSchema spec
> are automatically resolved. How to reuse XSchema "modules"; specifying
> intelligent defaults; mixing namespaces within a document; etc.
>
> - Time to implementation.
>
> We get a strong, flexible, powerful schema mechanism with robust
> implementations, immediately. I don't doubt the ability of the
> XSchema WG to
> come up with a good recommendation, but how long would it take
> until we see
> it implemented properly?
>
> - Market acceptance.
>
> By tying schemas to XSLT, every time a company uses one, it automatically
> can make use of the other. This would increase the market penetration of
> both recommendations. The schema recommendation stands to make most of the
> advantage; given that XSLT processors would be available in browsers and
> servers as a matter of course, this would significantly lower the barrier
> for performing validation, as compared to obtaining a separate schema
> processor
>
> How about it?
>
>     Oren Ben-Kiki
>
>
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