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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 17:41:35 -0500
Cc: Ivan Herman <ivan@w3.org>, RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <96DDA940-0B6D-42CB-8775-AD9FE512B0F7@ihmc.us>
To: Kingsley Idehen <kidehen@openlinksw.com>

On Apr 14, 2011, at 2:28 PM, Kingsley Idehen wrote:

>> 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,
> 
> Is an Address something?

I'd say, yes. But ...

> I think this matter might ultimately boil down to that question.

... I don't think so. The issue is, SPARQL users want to be able to use any URI to 'identify' an RDF graph inside an RDF dataset. Including for example a URI that is the name of a person, say. So the WG decided that this SPARQL-specific use of URIs was to be made independent from the RDF semantic meaning. But when the URI is used inside RDF, the RDF semantic rules apply to it, so this SPARQL-specific meaning no longer applies. 

> Methinks, an Address is the name of a Location.

I agree that makes good sense. Although there are those who would want to say it is the name of whatever is in the location :-)

Pat


> Thus, a URL is the use of a URI to name a Data Access Location -- a Data Source Name (DSN) in other data access technology quarters.
> 
> Ivan: What about the Object in a wdrs:describedby relation? Methinks, that would be an Address, which is the Name of a Location i.e., a g-box using Sandro's graph nomenclature.
> 
> If we can solve this riddle, we have one less problem re. Linked Data, RDF, and SPARQL :-)
> 
> 
> Kingsley
>> 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.ushttp://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.ushttp://www.ihmc.us/users/phayes
>> 
>> 
>> 
>> 
>> 
>> 
>> 
> 
> 
> -- 
> 
> Regards,
> 
> Kingsley Idehen	
> President&  CEO
> OpenLink Software
> Web:http://www.openlinksw.com
> Weblog:http://www.openlinksw.com/blog/~kidehen
> Twitter/Identi.ca: kidehen
> 
> 
> 
> 
> 
> 
> 
> 

------------------------------------------------------------
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
Received on Thursday, 14 April 2011 22:42:08 GMT

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