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Re: Multiple GRDDL results in a single transform??? GRDDL and Named Graphs

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Thu, 24 Jan 2008 13:27:50 -0500
Message-ID: <4798D8A6.5070301@ibiblio.org>
To: "Booth, David (HP Software - Boston)" <dbooth@hp.com>
Cc: Jeremy Carroll <jjc@hpl.hp.com>, "public-grddl-wg@w3.org" <public-grddl-wg@w3.org>, "patrick.stickler@nokia.com" <patrick.stickler@nokia.com>, "chris@bizer.de" <chris@bizer.de>, Phil Archer <parcher@icra.org>

I think it's up to the POWDER Group to decide whether or not to use
RDF/XML+GRDDL->RDF plus reification or vanilla XML+GRDDL->RDF plus
reification. As GRDDL Chair, I support any use of GRDDL :)

It's seems reification needs to be use to define the formal semantics of
POWDER, but I think it is the appropriate way to do it. Jeremy's
RDF->GRDDL->RDF solution is very clever, but developers might want a
vanilla XML version as well.

I would prefer not to revisit the test-cases (as we closed this issue
quite a while back, and I can see how the feature that Jeremy is
suggesting using could be useful, as analogous problems re entailment
crop up in OWL inference).  I think the point to remember is that
RDF/XML is, well, a valid XML format and so GRDDL can be applied to it,
and the point in the spec about "If F and G are GRDDL results of IR,
then the merge [RDF-MT] of F and G is also a GRDDL result of IR.".

Booth, David (HP Software - Boston) wrote:
> Thanks, the examples are quite helpful.  I was not aware that it was possible to do that with RDF/XML.
>
> While I definitely think a GRDDL-based approach is a good way to go, there are a couple of aspects of doing a GRDDL transformation of RDF/XML to produce more RDF that make me uncomfortable.
>
> 1. It relies on a corner feature of RDF/XML, though perhaps it is only a corner feature to me.  Maybe to others it is a central feature.  :)
>
> 2. It makes the semantics of an RDF/XML document less clear, because to a non-GRDDL aware receiver, the document conveys only the triples directly serialized in the RDF/XML, whereas to a GDDL-aware receiver, it conveys additional triples.  If a document is served as application/rdf+xml, the recipient should be able to look at the RDF/XML spec to determine its semantics.  But the RDF/XML spec does not reference the GRDDL spec.
>
> To an extent, we can finesse this ambiguity by recalling GRDDL's "faithful rendition" clause
> http://www.w3.org/TR/grddl/#sec_rend
> and taking the position that if the additional triples from the GRDDL transformation are all *entailments* from the base triples, then the resulting merged set of triples could legitimately be viewed as a "faithful rendition" of the original document.  However, that is very error prone, because essentially the same information is being conveyed in two different ways: once through the directly serialized triples and their entailments, and again through the GRDDL results.
>
> So regarding POWDER, I would be quite uncomfortable with POWDER using this RDF/XML + GRDDL approach.  I also don't see any benefit to it over an XML + GRDDL approach.  To be clear, by an "XML + GRDDL" approach I mean: define POWDER in terms of abstract RDF, but also define a custom XML format whose semantics are *entirely* defined by the RDF resulting from its GRDDL transformation.  This would give the combined benefits of:
>
>  - a concise XML serialization for those who want it, so XML tools can be used if desired;
>
>  - clear semantics (given by GRDDL-generated RDF); and
>
>  - compatibility with the Semantic Web, so standard RDF tools can also be used.
>
> Regarding GRDDL, I think it was a mistake to include that feature in the GRDDL spec.  I think it would have been better to say that the GRDDL results of an RDF/XML document -- or any other RDF serialization, for that matter -- are *only* the RDF graph represented by that document.
>
> In any event, GRDDL test case http://www.w3.org/TR/grddl-tests/#grddlonrdf is clearly flawed and should be corrected or deleted in an erratum, because the GRDDL spec at
> http://www.w3.org/TR/grddl/#rule_rdfxbase
> talks about a "conforming RDF/XML document"
> http://www.w3.org/TR/grddl/#rule_rdfxbase
> but, assuming the RDF Validator is correct, the input of that test case is not a conforming RDF/XML document.
>
>
> David Booth, Ph.D.
> HP Software
> +1 617 629 8881 office  |  dbooth@hp.com
> http://www.hp.com/go/software
>
> Opinions expressed herein are those of the author and do not represent the official views of HP unless explicitly stated otherwise.
>
>
>   
>> -----Original Message-----
>> From: Jeremy Carroll [mailto:jjc@hpl.hp.com]
>> Sent: Wednesday, January 23, 2008 6:00 AM
>> To: Booth, David (HP Software - Boston)
>> Cc: public-grddl-wg@w3.org; patrick.stickler@nokia.com;
>> chris@bizer.de; Phil Archer
>> Subject: Re: Multiple GRDDL results in a single transform???
>> GRDDL and Named Graphs
>>
>> Booth, David (HP Software - Boston) wrote:
>>
>>     
>>> Can you please show an example?  If the input for test case
>>> http://www.w3.org/2001/sw/grddl-wg/td/grddl-tests#grddlonrdf
>>> were converted to this form, what would it look like?
>>>
>>>       
>> Sorry for delay in replying ...
>> http://www.w3.org/2001/sw/grddl-wg/td/grddlonrdf.rdf doesn't include a
>> typed node ...
>>
>> This means that we can't use the namespace doc method but
>> (referring to
>> http://www.w3.org/TR/rdf-syntax-grammar/#start
>> )
>> We can serve the following doc with mimetype application/rdf+xml:
>>
>> <rdf:Description
>> xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>> xmlns:foaf="http://xmlns.com/foaf/0.1/"
>> xmlns:con="http://www.w3.org/2000/10/swap/pim/contact#"
>> xmlns:data-view="http://www.w3.org/2003/g/data-view#"
>> data-view:transformation="foaf2con.xsl"
>> rdf:about="http://musicbrainz.org/mm-2.1/album/6b050dcf-7ab1-4
>> 56d-9e1b-c3c41c18eed2">
>> <foaf:maker>
>> <foaf:Agent
>> rdf:about="http://musicbrainz.org/mm-2.1/artist/33b3c323-77c2-
>> 417c-a5b4-af7e6a111cc9">
>> <foaf:name>The Jimi Hendrix Experience</foaf:name>
>> </foaf:Agent>
>> </foaf:maker>
>>
>> </rdf:Description>
>>
>> This has one extra triple over and above the original, since the
>> data-view:transformation is treated as a property attribute.
>>
>> Adding a type triple instead, we could also serve the
>> following as rdf/xml:
>>
>>
>> <eg:DummyType
>> xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>> xmlns:foaf="http://xmlns.com/foaf/0.1/"
>> xmlns:con="http://www.w3.org/2000/10/swap/pim/contact#"
>> xmlns:eg="http://example.org/namespace#"
>> rdf:about="http://musicbrainz.org/mm-2.1/album/6b050dcf-7ab1-4
>> 56d-9e1b-c3c41c18eed2">
>> <foaf:maker>
>> <foaf:Agent
>> rdf:about="http://musicbrainz.org/mm-2.1/artist/33b3c323-77c2-
>> 417c-a5b4-af7e6a111cc9">
>> <foaf:name>The Jimi Hendrix Experience</foaf:name>
>> </foaf:Agent>
>> </foaf:maker>
>>
>> </eg:DummyType>
>>
>> And at http://example.org/namespace.rdf we have a namespace doc
>> including the triple
>>
>> <http://example.org/namespace#>
>>   dataview:namespaceTransformation
>>   <????/foaf2con.xsl> .
>>
>> Jeremy
>>
>>
>>
>>
>>
>>
>>
>>     
>
>
>   


-- 
		-harry

Harry Halpin,  University of Edinburgh 
http://www.ibiblio.org/hhalpin 6B522426
Received on Thursday, 24 January 2008 18:27:39 UTC

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