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Re: Comments on GRDDL (using 3rd-party XML schemas with GRDDL) [OK?]

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Tue, 24 Jul 2007 20:24:05 -0400
Message-ID: <46A69825.8080506@ibiblio.org>
To: "C. M. Sperberg-McQueen" <cmsmcq@acm.org>
Cc: Dan Connolly <connolly@w3.org>, Andrew Eisenberg <andrew.eisenberg@us.ibm.com>, public-grddl-comments@w3.org, w3c-xsl-query@w3.org

C. M. Sperberg-McQueen wrote:
> On 24 Jul 2007, at 10:38 , Harry Halpin wrote:
>> ...
>> I understand that's a perfectly sensible use-case, but not for GRDDL as
>> it stands. There is a technical difficulty: Since the schema is not at
>> the namespace document and not marked up in the document, how would the
>> GRDDL processor ever discover your schema annotations by "following its
>> nose" from the source document?
> I imagine it happening the same way it happens for schema
> processors.  Different schema processors do it differently;
> possible mechanisms include invocation-time parameters,
> catalogs, local repositories, well-known locations,
> dereferencing the namespace name, and of course hints in
> the document.
> From this discussion I understand that if a GRDDL processor
> allows me to specify where to find schema documents I'd like
> to use, then that processor doesn't conform to the GRDDL
> spec.  That seems a shame to me.
We do not forbid GRDDL agents from allowing "local policy" to provide
additional parameters for GRDDL processing - in fact, we go through
great pains in the specification and the test-suite to allow local
policy to determine certain types of processing as regards security and
processing, and it is under this rubric that one could imagine a local
policy specifying that all documents of vocabulary X use transformation
associated with a schema at the non-namespace document location Y
through an additional parameter. However, as GRDDL is an intentionally
lightweight specification that purposively avoided adding additional
required parameters, we did not *require* GRDDL-aware agents to have
this parameter, as GRDDL-aware agents may have *no parameters*.

So,  a GRDDL-aware agent could have additional parameters specifying
schemas and transformations locations in accordance with local policy,
and *still be a conformant GRDDL specification* as long as it passes our
test-suite. However, we do not specify this sort of behavior in out
test-suite, as it would be local policy.
>> For your use-case, since the location of the schema and associated with
>> is known by you, but not described the document or namespace document,
>> it would make more sense to explicitly write your transformation to RDF
>> for the type of vocabulary using something like XProc [2] I think rather
>> than GRDDL, or simply use the transformation using a processing language
>> like XSLT or XQuery directly.
>> The only solution would be to add an arbitrary parameter to GRDDL.
>> However, we have endeavored in the WG to make GRDDL "parameter-free" and
>> instead rely on "following-your-nose"  and "following other specs" to
>> find the transformation, and if one wants to add an parameter to GRDDL
>> to locate a transformation, one should just use the processing language
>> like XSLT or XQuery locally and directly rather than relying on GRDDL,
>> since there is no advantage using GRDDL would provide in this case over
>> existing software.
>> Does this answer satisfy you?
> It comes a lot closer, thanks.  If the GRDDL spec anywhere says
> roughly what you say in the preceding few paragraphs, I think I
> probably am satisfied; I'll need to sleep on it to be sure.
> (And of course I do not speak for the XML Query and XSL WGs.
> Satisfying me is probably a good step toward satisfying the WGs,
> but they are distinct concepts.)
Thanks - do get back to me once this answer satisfies you. If you wish
for a particular sentence(s) to be added to the specification specifying
this, please specify those sentences.

Note re your and Chime's dialogue about authority, note that *of course*
a schema at a location somewhere besides the URI of the may be
authoritative. However, it may also just not be found a GRDDL-aware
agent. We imagine for your use-case that authors will likely use XQuery
or XSLT directly, perhaps in combination with XProc, or possibly some
GRDDL-aware agent whose local policy specifies a transformation.

> Michael


Harry Halpin,  University of Edinburgh 
http://www.ibiblio.org/hhalpin 6B522426
Received on Wednesday, 25 July 2007 00:24:49 UTC

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