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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: Thu, 14 Apr 2011 16:50:30 -0500
Cc: Ivan Herman <ivan@w3.org>, RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <57BCCDE9-7A90-4156-9838-E16CC94C93B0@ihmc.us>
To: antoine.zimmermann@insa-lyon.fr, Antoine Zimmermann <antoine.zimmermann@gmail.com>

On Apr 14, 2011, at 2:36 PM, Antoine Zimmermann wrote:

> Our decision today was about SPARQL datasets and what the URI in the
> <n,G> pairs is referring to. We said it does not necessarily identify the graph in the sense of what the RDF semantics says (the interpretation of n does not need to be the graph). This is enough to define a notion of interpretation and model of a dataset, as explained in section "Interpreting datasets" of http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/RDF-Datasets-Proposal.

Oh, wait. We did NOT agree to accept an alien model theory for datasets. If you wish to propose this, please make it an action item for the WG. I will argue strongly, and vote, against it. But in any case, the proposed model theory for datasets, in the proposal, uses the same language or reference in an interpretation, so does not resolve the issue I was pointing out. 

> 
> Now, the use cases clearly show that we need a way to identify a graph (or rather a g-box) with a URI. My understanding was that this is independent from today's decision, and I hope it is.

Quite. And if it is, then this use of a URI to identify a graph (g-box, whatever) will be independent of the SPARQL use of URIs to identify graphs. And hence, my point about the use of URIs in RDF triples will still stand. 

So all is not good, unless you are in agreement that SPARQL cannot use the same identifier in an RDF object position and also to identify a graph in a dataset. 

Pat

> 
> So all is good so far.
> 
> 
> Le 14/04/2011 19:09, Pat Hayes a écrit :
>> Well, the use of a URI inside an RDF triple assumes that the URI is
>> being used as a name, to refer to something. Using a URI which is the
>> name of a named graph, for example, would refer to the graph. But in
>> this decision we *explicitly* say that this is *not* how the SPARQL
>> association of URIs to graphs works: that the 'associated' graph
>> which is 'tagged' (if I have that right) by a URI might well not be
>> the entity referred to by the URI. The example was given in which the
>> URI is the name of a person, ie refers to a person, and still can be
>> used to 'tag' a graph for SPARQL purposes. If such a URI is used as
>> the object of an RDF triple, it will refer to the person, not to the
>> SPARQL-tagged graph. As there is no way to know whether the graph
>> that is SPARQL-tagged by a URI is, or is not, the referent of the
>> URI, any use of that URI as a name inside an RDF triple must be
>> basically unrelated to its use as a SPARQL graph tag; or at any rate,
>> that is the only safe assumption to make.
>> 
>> In a nutshell, RDF uses URIs as referring names. Apparently, SPARQL
>> does not, when it comes to identifying graphs. So the uses of URIs in
>> RDF triples and in SPARQL tags are dissociated from one another, and
>> need have no relationship. So, no relationship can be relied upon.
>> The 'naming' of graphs in SPARQL is a wholly SPARQL-local business,
>> unrelated to RDF semantics and therefore to any RDF content.
>> 
>> I assumed this was obvious at the time we were discussing this, by
>> the way. But I confess I had not at that time read the Wiki proposal
>> fully, and not seen the 'imports' examples.
>> 
>> Pat
>> 
>> On Apr 14, 2011, at 11:55 AM, Ivan Herman wrote:
>> 
>>> Pat,
>>> 
>>> sorry, but you will have to explain (me) what the problem is.
>>> 
>>> Ivan
>>> 
>>> ---- Ivan Herman web: http://www.ivan-herman.net mobile: +31 64
>>> 1044 153
>>> 
>>> On 14 Apr 2011, at 18:43, Pat Hayes<phayes@ihmc.us>  wrote:
>>> 
>>>> I note in passing that the Proposed WG Decision dated 14 April
>>>> has the consequence that the IRi associated with a graph in
>>>> SPARQL cannot be used inside an RDF triple to reliably refer to
>>>> the graph. This means in particular that uses such as those
>>>> contemplated in
>>>> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/RDF-Datasets-Proposal,
>>>> which use the SPARQL name as the object in an 'imports' triple,
>>>> are ruled out by this decision.
>>>> 
>>>> Pat
>>>> 
>>>> On Apr 13, 2011, at 4:29 AM, RDF Working Group Issue Tracker
>>>> wrote:
>>>> 
>>>>> 
>>>>> ISSUE-30: How does SPARQL's notion of RDF dataset relate our
>>>>> notion of multiple graphs?
>>>>> 
>>>>> http://www.w3.org/2011/rdf-wg/track/issues/30
>>>>> 
>>>>> Raised by: On product:
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>> 
>>>> ------------------------------------------------------------ IHMC
>>>> (850)434 8903 or (650)494 3973 40 South Alcaniz St.
>>>> (850)202 4416   office Pensacola
>>>> (850)202 4440   fax FL 32502
>>>> (850)291 0667   mobile phayesAT-SIGNihmc.us
>>>> http://www.ihmc.us/users/phayes
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>> 
>> ------------------------------------------------------------ IHMC
>> (850)434 8903 or (650)494 3973 40 South Alcaniz St.
>> (850)202 4416   office Pensacola                            (850)202
>> 4440   fax FL 32502                              (850)291 0667
>> mobile phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>> 
>> 
>> 
>> 
>> 
>> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
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Received on Thursday, 14 April 2011 21:51:07 GMT

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