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

From: C. M. Sperberg-McQueen <cmsmcq@acm.org>
Date: Thu, 26 Jul 2007 17:29:02 -0600
Message-Id: <E2F92660-116C-4017-84F6-21CF3D84BFE9@acm.org>
Cc: "C. M. Sperberg-McQueen" <cmsmcq@acm.org>, Jonathan Robie <jonathan.robie@redhat.com>, Dan Connolly <connolly@w3.org>, Andrew Eisenberg <andrew.eisenberg@us.ibm.com>, public-grddl-comments@w3.org, w3c-xsl-query@w3.org, "Ogbuji, Chimezie" <OGBUJIC@ccf.org>
To: Harry Halpin <hhalpin@ibiblio.org>

On 26 Jul 2007, at 07:27 , Harry Halpin wrote:

> Jonathan Robie wrote:
>> Harry Halpin wrote:
>>> 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.
>> This may point to a solution. The W3C XML Schema spec allows
>> implementations great freedom in how they do - or do not - locate a
>> schema for a given namespace used in an XML document. This is
>> specified in *http://www.w3.org/TR/xmlschema-1/#schema_reference.
>> A GRDDL-aware agent could either dereference the URL directly to see
>> if there is a schema there, or use any other means at its disposal to
>> find a schema that governs a namespace used in a document. From what
>> you say above, I don't think this would actually change the  
>> definition
>> of GRDDL, but saying this would be helpful to those who use W3C XML
>> Schema. Of course, you can't require GRDDL processors to use any
>> particular strategy, or insist that they actually find a schema, but
>> the XML Schema specification doesn't do that either.
>> If you said this in the spec, I think I personally would be
>> satisified. (I speak neither for Michael nor for the Working Group.)

> This ability to use "3rd-party" schemas would clearly be an optional
> feature of local policy. Now, the GRDDL specificiation only mentions
> local policy briefly in regards to security. However, the GRDDL
> Test-Cases Proposed Rec has a section on local policy[1].
> Would adding the sentence in [brackets] satisfy both you, Michael, and
> the Working Group:
> "The GRDDL specification states that any transformation identified  
> by an
> author of a GRDDL source document will provide a Faithful Rendition
> <http://www.w3.org/TR/grddl/#sec_rend> of the information expressed in
> the source document. The specification also grants a GRDDL-aware agent
> the license <http://www.w3.org/TR/2007/WD-grddl-20070302/#sec_agt> to
> makes a determination of whether or not to apply a particular
> transformation guided by user interaction, a local security policy, or
> the agent's capabilities. [For example, a GRDDL-aware agent may have a
> security policy that prevents it from accessing GRDDL transformations
> located in untrusted domain names, it may be unable to apply
> transformations given in a language it does not support, and it may
> feature additional non-normative capabilities such as allowing
> transformations to be found in schemas not specified at the namespace
> document.]  However, in defining these tests it was assumed that the
> GRDDL-aware agent being tested is using a security policy which does
> *not* prevent it from applying transformations identified in each test
> [, supports XSLT 1.0, and does not rely on any capabilities outside
> those defined in the GRDDL Specification]. Such an agent should  
> produce
> the GRDDL result associated with each normative test, except as
> specified immediately below."

It does satisfy me.  I will ask at the joint meeting of XSL
and XML Query next Tuesday that the groups confirm that
it satisfies them.

Thank you.

--Michael Sperberg-McQueen
Received on Thursday, 26 July 2007 23:29:13 UTC

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