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   Re: [xml-dev] Re: Flexible Schemas (was RE: [xml-dev] The task to be sol

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At 01:55 PM 19/01/02 +0100, Nicolas Lehuen wrote:
>As I've said three of four times now, show me the algorithm that will find
>the URL of the RDDL document for this document : http://www.rddl.org/. This
>is a FONDAMENTAL problem with RDDL.

1. Ascertain the namespace of the root element
2. Dereference that namespace

In the case of that document, the namespace of the root element is
http://www.w3.org/1999/xhtml.  Dereferencing this reveals that
there is no RDDL posted for XHTML.  What a pity.

But in general your question is slightly mis-phrased.  RDDL isn't
designed to be associated with a *document* but with a *namespace*
which in practical terms means an element or attribute.  Thus when
I read through the document you reference, eventually I come to
an element that's in the namespace http://www.rddl.org/ - this
namespace is lucky enough to have a RDDL directory available.  

As many people have pointed out, modern XML resources can 
have lots of different namespaces.  RDDL is designed to help
in the case where you don't know about one or more of them. -Tim

>> Instead I think it suggests that our approach to writing *schemas* isn't
>> flexible enough to deal with documents containing an arbitrary mix of
>> namespaces. I should state up front I don't have any answers here,
>> I'm just interested in a general discussion.
>> The majority of schemas that I've seen assume a fixed set of
>> elements. These elements may come from zero, one or more namespaces.
>> The schema is "closed". They're designed to validate a particular
>> class of documents.
>> Some schemas are "open", i.e. they allow "unknown" elements to be
>> used in the document, and these usually in fairly fixed places (cf: XSD
>> ANY, XHTML DTD Modularization). However these schemas still seem
>> to be designed to validate _documents_. They validate the document,
>> and ignore sections of it, or as with modularization defer to other
>> schema/dtd modules.
>> Yet the scenario you're discussing is one which seems like it could
>> become increasingly common: we have a mixed namespace document
>> for which there is no schema. You're asking, how can I validate
>> these documents? Is there a heuristic for combining together several
>> schemas to achieve this goal?
>In fact there are schemas for RDDL and WAP 2.0, DTD are provided for both
>examples. Nothing prevents a schema from manipulating names from different
>namespaces. However, the scenario I'm discussing is a scenario where the
>document has not a single namespace, breaking the false but too often
>believed assumption that a namespace name is equivalent to a DOCTYPE
>Regarding "open" schema, that is to say schema that are meant to be extended
>or inherited, there is indeed a problem. I think namespaces are part of the
>solution, but are in no way THE solution.
>> To do this you need to define schemas not only to be open, but also
>> to be easily fragmented so that portions of it can be applied. I can
>> imagine doing this with a schematron schema (only apply certain
>> but not with a DTD. I also assume there's a way to do this with RELAX NG
>> and XSD. You then need to apply these fragments to the document to
>> validate it.
>Yeah, I think that in opened schemas, partial validation of "patterns" are
>required, instead of global validation of whole documents. This can be done
>with the current schema languages, though, even DTDs. I tried to write down
>some thoughts about it there :
>> I don't see schemas being written with this use in mind, nor do I see
>> validators that allow this flexible application of schemas.
>> I may be showing a lack of understanding here, I don't mind
>> looking a fool :) Does anyone else see this as an issue, or is it
>> not a problem? Am I misunderstanding something?
>> RDDL only enters this picture as a way to associate a schema, or
>> fragment thereof with a Namespace URL. Doing something with those
>> fragments, assuming they're available is something for the validator.
>Schemas can be associated to namespace (one or many namespaces), but the
>contrary is, IMHO, a bad idea. I am sorry, but I don't see how to solve this
>problem without relying on the concept of document or element type. I'll try
>to expand on this in the article mentionned above.
>> Cheers,
>> L.
>> --
>> Leigh Dodds, Research Group, Ingenta | "Pluralitas non est ponenda
>> http://weblogs.userland.com/eclectic |    sine necessitate"
>> http://www.xml.com/pub/xmldeviant    |     -- William of Ockham
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