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Re: comments on RDF-Datasets-Proposal

From: Antoine Zimmermann <antoine.zimmermann@insa-lyon.fr>
Date: Wed, 29 Jun 2011 10:24:16 +0200
Message-ID: <4E0AE130.4000701@insa-lyon.fr>
To: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
CC: "public-rdf-wg@w3.org" <public-rdf-wg@w3.org>
Ok, I was not clear enough. The section named "Semantic extension" 
should be deleted and forgotten. It is outdated.

I maintain that I'm happy with "graph names" used loosely, like

:me { :me a foaf:Person }

If I want to import a graph to the one "named" :mydog, I would do it as 
follows, assuming that importing is defined adequately:

:G1 :hasGraphIRI "http://..../me"^^xsd:anyURI .
:G2 :hasGraphIRI "..."^^xsd:anyURI .
:G1 :imports :G2 .
# and if you want:
:G2 owl:sameAs :G3 .

:G1, :G2 and :G3 denote graphs, i.e., their RDF interpretations are sets 
of triples. :G2 and :G3 denote the same set of triples. But this only 
hold in a world where :imports is properly defined and this importing 
mechanism is certainly not the same as owl:imports.

Anyway, this has its own problems too.

Le 29/06/2011 10:02, Pierre-Antoine Champin a écrit :
> Antoine,
>
> On 06/28/2011 12:07 PM, Antoine Zimmermann wrote:
>> Pierre-Antoine,
>>
>> Le 22/06/2011 19:19, Pierre-Antoine Champin a écrit :
>>> Hi all,
>>>
>>> after today's telecon, I read the proposal at [1].
>>>
>>> First, it seems to be a "light" version of the Named Graph paper that
>>> Pat mentionned. "Light", because it specifies that
>>>
>>> "The interpretation of the IRI [paired to graphs], in the RDF Semantics
>>> sense, is left unspecified."
>>>
>>> It is all very well, but what happens when one wants to use those IRIs
>>> *in* the named graphs? As proposed in the 'Semantic Extension' section
>>> of [1]?
>>
>> This section, which I wrote, was put there before we made any decision
>> on what the naming mechanism of graph store means. This section should
>> be considered informative, explaining how the basic semantics can be
>> extended. Such extension /may/ be defined externally to this WG.
>>
>> The semantics is extremely simple and does not make any assumption on
>> what the "name of the graph" means. The graph name is just used as an
>> indice in a family of graphs.
>
> I'm affraid you can not avoid to make that assumption. If I follow you,
>
>    :G1 graph:imports :G2 .
>
> would "only" mean
>
>    the graph associated with URI :G1 imports the graph associated with
>    URI :G2 (for some given association which is not *naming*)
>
> Now assume that you know that
>
>    :G2 owl:sameAs :G3 .
>
> Nothing prevents you from infering now that
>
>    :G1 graph:imports :G3 .
>
> But the graph associated with URI :G2 may be completely different from
> the graph associated with URI :G3 !
>
> The problem comes from the fact that, to avoid the "graph naming
> assumption", we need a property to talk about the URIs (and indirectly,
> about the graph associated with them) while RDF properties always talk
> about the resources denoted by the URIs.
>
> If we used *resources* as graph identifiers, then it would be different.
> But unfortunately, that is not what SPARQL is doing.
>
>    pa
>
>
>
>>
>>
>>>
>>> Stating
>>>
>>>     :G1 graph:imports :G2
>>>
>>> does make some assumption about the meaning of :G1 and :G2 in the RDF
>>> Semantics! More generally, if we want to make graphs first class
>>> citizens of RDF, we need a mean to talk about them, hence we need IRIs
>>> whose interpretation in RDF Semantics is that graph.
>>>
>>>     pa
>>>
>>>
>>> [1] http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/RDF-Datasets-Proposal
>>>
>>
>>
>


-- 
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 Wednesday, 29 June 2011 08:24:46 GMT

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