W3C home > Mailing lists > Public > public-rdf-dawg@w3.org > October to December 2009

Re: [TF-ENT] Querying datasets with default plus named graphs

From: Ivan Herman <ivan@w3.org>
Date: Thu, 08 Oct 2009 14:44:41 +0200
Message-ID: <4ACDDEB9.2060207@w3.org>
To: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
CC: Axel Polleres <axel.polleres@deri.org>, "Seaborne, Andy" <andy.seaborne@hp.com>, SPARQL Working Group <public-rdf-dawg@w3.org>


Birte Glimm wrote:
> 2009/10/8 Ivan Herman <ivan@w3.org>:
>> Axel Polleres wrote:
> [snip]
>>> +1 to keep entailments local to the separate  graphs in the DS
>>> (<chairhatoff> although  I  personally consider it a drawback that you
>>> can't refer to ontologies from named graphs)
>> Hm. Yes, this seems to be a consequence which is a bit disagreeable
>> indeed:-(
>>
>> In OWL, I can of course use owl:import in my WHERE clause (Birte, this is
>> all right, isn't it?) which is not that bad, the user has to make things
>> explicit. But this does not help the RDFS case.
> 
> In OWL you can use imports, but I suppose you mean FROM and not WHERE
> clause. If the ontology you are querying (as given in the FROM (NAMED)
> clause) contains imports, then all imports will be loaded and the
> axioms from the imported ontologies will be taken into account for
> finding the query answers.
>

No, I actually meant putting an owl:import into the WHERE clause. Would 
that be possible? If I simply look at it as an RDF statement than that 
would be part of the overall graph, just as I can add an RDF triple in 
the WHERE clause...

I am not worried about the OWL case. More of the RDFS case: how does 
FROM NAMED and RDFS cooperate (there is no import statement...)


>> It also raises an issue on the RIF side. RIF rules cannot be expressed in
>> RDF. How would one add RIF rules to an entailement regime if we wanted to
>> cover RIF? It might be a showstopper for that case:-(
> 
> In my total RIF naivity, I would assume you can say:
> 
> SELECT ?o FROM <http://example.org/myrules.rif> WHERE { :s :p ?o . }
> 
> Here I assume that myrules.rif contains the rules and references
> (imports) for the relevant RDF graphs. In the RIF OWL compatibility
> doc it says:
> 
> A RIF document that refers to (imports) RDF graphs and/or RDFS/OWL
> ontologies, or any use of a RIF document with RDF graphs, is viewed as
> a combination of a document and a number of graphs and ontologies.
> This document specifies how, in such a combination, the document and
> the graphs and ontologies interoperate in a technical sense, i.e., the
> conditions under which the combination is satisfiable (i.e.,
> consistent), as well as the entailments (i.e., logical consequences)
> of the combination. The interaction between RIF and RDF/OWL is
> realized by connecting the model theory of RIF [RIF-BLD] with the
> model theories of RDF [RDF-Semantics] and OWL [OWL2-Semantics],
> respectively.
> 
> In my example, I assume that myrules.rif is such a document as
> mentioned above and you would query the RDF graphs pls the entailmens
> that you get from the rules.
> 

And what you say is perfectly o.k. in view of the RIF specification. 
However: in SPARQL, FROM and FROM NAMED are defined  to specify RDF 
datasets. OWL and RDFS are (or can be expressed in) RDF. RIF rules cannot.

That actually may create problems for OWL, too. There is no problem if 
the OWL ontology in the FROM clause is in RDF. But would the spec allow 
to refer too OWL ontologies in functional and/or Manchester syntax via 
the FROM or FROM NAMED clauses?

I would expect we should be able to do that, but that might affect the 
query language specification.

I remember Axel and I had some corridor chat at some point that would 
allow adding a media type to the FROM (NAMED) clause...

Ivan

> Birte
> 
>> Ivan
>>
>>
>> --
>>
>> Ivan Herman, W3C Semantic Web Activity Lead
>> Home: http://www.w3.org/People/Ivan/
>> mobile: +31-641044153
>> PGP Key: http://www.ivan-herman.net/pgpkey.html
>> FOAF: http://www.ivan-herman.net/foaf.rdf
>>
> 
> 
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf

Received on Thursday, 8 October 2009 12:41:36 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:15:40 GMT