W3C home > Mailing lists > Public > public-rdf-wg@w3.org > June 2011

Re: comments on RDF-Datasets-Proposal

From: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
Date: Wed, 29 Jun 2011 14:28:39 +0200
Message-ID: <4E0B1A77.9070206@liris.cnrs.fr>
To: "antoine.zimmermann@insa-lyon.fr" <antoine.zimmermann@insa-lyon.fr>
CC: "public-rdf-wg@w3.org" <public-rdf-wg@w3.org>
On 06/29/2011 10:24 AM, Antoine Zimmermann wrote:
> 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 It is outdated.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 }

don't get me wrong, I'm perfectly happy with it myself, as long as we
are clear.

> 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 .

ah, but this is a totally different thing now :)
and with that I'm perfectly happy as well.

My concern is that it does not match common SPARQL usages:
if you were to build the import-closure of some graph, would you rather
write

  CONSTRUCT { ?s ?p ?o }
  WHERE {
      :me graph:import ?g .
      GRAPH ?g { ?s ?p ?o }
  }

or

  CONSTRUCT { ?s ?p ?o }
  WHERE {
      [ :hasGraphIRI "...me"^^xsd:anyURI ]
      graph:imports
      [ :hasGraphIRI ?guri ]
      GRAPH ?gres { ?s ?p ?o }
      FILTER (str(?gres) = str(?guri))
  }

?
And more importantly, what do you think the average SPARQL user would
rather write?

    pa


> 
> :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
>>>>
>>>
>>>
>>
> 
> 
Received on Wednesday, 29 June 2011 12:29:37 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:25:44 GMT