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

From: Antoine Zimmermann <antoine.zimmermann@insa-lyon.fr>
Date: Fri, 15 Apr 2011 11:18:20 +0200
Message-ID: <4DA80D5C.4060601@insa-lyon.fr>
To: Pat Hayes <phayes@ihmc.us>
CC: RDF Working Group WG <public-rdf-wg@w3.org>
Le 14/04/2011 23:50, Pat Hayes a écrit :
>
> 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.

The proposed semantics for datasets does not forbid defining a mechanism 
to identify graphs. What Pierre-Antoine describes in his email would 
work, I believe.

What is written in "Interpreting datasets" is probably the least 
constrained form of semantics you can define for a dataset, based on RDF 
interpretations. It fulfils the need for having diverging opinions 
expressed in different graphs (or even contradicting graphs) and if some 
people want more constraining semantics, it's not a problem to extend 
it. If we don't define the semantics, I'm afraid there's going to be 
endless discussions or misunderstanding about what the stuff in the 
dataset entails.

>>
>> 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.

I do not see what is the problem of having URIs that identify graphs (in 
the RDF interpretation sense) together with additional labels for graphs 
which just happen to be URIs too.

:antoine { :g  a  :Graph . :antoine a :Person }

works for me. If I want I can (for my personal purpose, not for the WG) 
extend the RDF interpretation with an additional "graph-map" which maps 
URIs to graphs such that a URI can identify a thing (a person, a cow, an 
idea) as well as a graph.
In OWL 2 DL, you have 3 interpretation functions that maps URIs to 
different things. An individual-interpration, a property-interpretation 
and a class-interpretation. These three interpretations can map the same 
URI to 3 distinct things, such that a URI "names" multiple things having 
a different nature.

Names map to things *in a context*. A URI names a thing in RDF by way of 
its RDF-interpretation but a URI can name a graph in a dataset by way of 
what is called "named graphs" in the SPARQL spec. I could also name my 
dog Tim Berners-Lee, or even name it using TimBL's URI and register this 
identification somehow and that would not be a problem for RDF 
(although, I agree, it would be silly).


AZ.

> 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 phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>
>
>
>
>


-- 
Antoine Zimmermann
Researcher at:
Laboratoire d'InfoRmatique en Image et Systèmes d'information
Database Group
7 Avenue Jean Capelle
69621 Villeurbanne Cedex
France
Tel: +33(0)4 72 43 61 74 - Fax: +33(0)4 72 43 87 13
Lecturer at:
Institut National des Sciences Appliquées de Lyon
20 Avenue Albert Einstein
69621 Villeurbanne Cedex
France
antoine.zimmermann@insa-lyon.fr
http://zimmer.aprilfoolsreview.com/
Received on Friday, 15 April 2011 09:18:50 GMT

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