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Re: ISSUE-30: How does SPARQL's notion of RDF dataset relate our notion of multiple graphs?

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 18 Apr 2011 13:02:35 -0500
Cc: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>, RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <544BED6B-F55B-48CD-AD00-74416B8FC3E7@ihmc.us>
To: Ivan Herman <ivan@w3.org>

On Apr 18, 2011, at 8:16 AM, Ivan Herman wrote:

> 
> On Apr 18, 2011, at 15:00 , Pierre-Antoine Champin wrote:
> 
> <snip/>
>>>> Not so easy. When you *use* a URI in RDF, like the <g> here, it is
>>>> not referring to itself, but to what it denotes. (Put another way,
>>>> the URI is not quoted.) Which means that rdf:tags isn't going to
>>>> have the meaning you intend. Now, we could change this, and say
>>>> that rdf:tag is (uniquely) referentially opaque in its subject
>>>> position. This would however be a major change to the RDF semantics
>>>> and data model, and would require us to re-wrote the semantic spec.
>>>> And it has other knock-on consequences eg for OWL, since OWL
>>>> equality reasoning would have to be blocked from such triples. So I
>>>> think we should think very hard before going there.
>>>> 
>>>> However, XML Schema has a datatype for making literals refer to
>>>> URIs. http://www.w3.org/TR/xmlschema-2/#anyURI  and we could use
>>>> that. OK, we can't have a literal in subject position (sigh), so we
>>>> have to turn it around:
>>>> 
>>>> <h> rdf:taggedBy xsd:anyURI^^"<the URI written as a string>" .
>>>> 
>>>> and then it would all work, without breaking the RDF semantics.
>>> 
>>> I understand, but isn't this problem a reflection of the fact that we
>>> try to model here the common term of tagging, ie, attaching a string
>>> to a resource as some sort of a characterization of the latter? In
>>> fact, as we said at the f2f, SPARQL is blissfully silent on how that
>>> URI is used. If we want to avoid misunderstandings through the usage
>>> of the word tagging, we can say something like
>>> 
>>> <g> rdf:loose_association_of_resources <h> .
>> 
>> nah...
>> 
>> <i> owl:sameAs <g> .
>> 
>> entails
>> 
>> <i> rdf:loose_assoctiation_of_resources <h> .
>> 
>> Is this what you want to say??
> 
> Hm. I do not know...
> 
> Given that SPARQL is loose in the way they use URI-s from graphs in datasets, I would not be shocked by this. The question is what would the SPARQL 1.1 entailment regime say about this. 
> 
> But, again: I wonder whether we have to say anything in formal terms at all about SPARQL's behaviour, except to make it clear that (<g>,G) is _not_ a shorthand for <g> identifying G.

But, Ivan, this thread began when *you* suggested using RDF to assert/declare something about SPARQL behavior. Which is exactly what is ruled out by this looseness. All Pierre-Antoine and I are doing is trying to take your idea and make it work in RDF. Are you now saying it was a bad idea all along, or are you saying that we don't need to do it using RDF, or what?

Pat

> 
> Ivan
> 
> 
>> 
>> I prefer Pat's proposa: if you want to associate something with a *uri*
>> (and not a resource), use a xsd:anyURI literal.
>> 
>>   pa
>> 
> 
> ----
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> PGP Key: http://www.ivan-herman.net/pgpkey.html
> FOAF: http://www.ivan-herman.net/foaf.rdf
> 
> 
> 
> 
> 

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Received on Monday, 18 April 2011 18:03:07 GMT

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