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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 12:38:18 -0400
Message-ID: <46A62AFA.8050000@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

On 18 Jul 2007, at 16:08 , Harry Halpin wrote:

>> An aside, although the official response will come from Dan himself.
>>
>> The reason GRDDL does not use third-party schemas is because it  
>> already has a mechanism (for both XHTML and XML) for pointing to  
>> third-party transformations. Since the only reason GRDDL uses  a  
>> schema at the namespace URI is to find a transformation (as it uses  
>> no other part of the schema), it seems reasonable to assume that if  
>> a  schema is somewhere else rather than at a namespace URI, then  
>> the user can simply directly point to the transformation given by  
>> the "third-party" schema. This keeps indirection to minimum.

> So if I have a few thousand, or a few hundred thousand, documents
> in the same vocabulary, and use a schema for that vocabulary which
> is not at the namespace name but which is accessible to my processes,
> the advice of the GRDDL group is not to document the transformation
> in the schema document, but to edit each document and add an
> explicit link to the GRDDL transformation for that vocabulary?
> Given that the semantics are associated with the vocabulary,
> and the annotations for the vocabulary are documented in the
> schema document I use -- and given that there's no particular
> technical difficulty involved here, that I can see -- why would
> I as a document owner want to incur that kind of cost and
> introduce that kind of redundancy?

> --C. M. Sperberg-McQueen

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?

We did also think about a similar use-case, as the GRDDL Use-Cases draft
mentions [1], but the proposed solution of linking to the transformation
relies on a HTTP Header Linking Draft that, well, seems to not be making
progress in the IETF.

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?

[1]http://www.w3.org/TR/grddl-scenarios/#header_use_case
[2]http://www.w3.org/TR/xproc/


-- 
		-harry

Harry Halpin,  University of Edinburgh 
http://www.ibiblio.org/hhalpin 6B522426
Received on Tuesday, 24 July 2007 16:38:56 GMT

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