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

From: Axel Polleres <axel.polleres@deri.org>
Date: Fri, 9 Oct 2009 07:59:26 +0100
Cc: Birte Glimm <birte.glimm@comlab.ox.ac.uk>, Andy Seaborne <andy.seaborne@hp.com>
Message-Id: <E902EAE6-208C-494C-B14E-6D858578A797@deri.org>
To: Ivan Herman <ivan@w3.org>, SPARQL Working Group <public-rdf-dawg@w3.org>
Ok, Will ask rif, whether those uris still can be given a more neutral  
name.

Axel

On 9 Oct 2009, at 06:12, Ivan Herman wrote:

> Hey Birte,
>
> On Thu, October 8, 2009 1:35 pm, Birte Glimm wrote:
> > [snip]
> >>>> 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...
> >
> > Well, but in the WHERE clause it maily "restricts" solutions,  
> i.e., I
> > will only return solutions that make the BGP true (possibly under  
> some
> > entailment regime). Now, if you write
> > SELECT * WHERE { ?x owl:imports ?y. }
> > That does not force the query processor to import anything under any
> > entailment regime, even if I were to replace the variables with IRIs
> > of ontologies. Under OWL DL (if I remember correctly), your ontology
> > would not even entail _:x owl_imports IRI_of_some_imported_ontology
> > (_:x being the  blank node that represents this ontology) because as
> > annotations, imports do not cause such an entailment. They are  
> rather
> > an imperative instruction that tell the reasoner that it should also
> > consider the axioms from the ontology that is imported. The axioms
> > will be taken into account for entailments, but neither annotations
> > nor imports can be queried if we require solutions to be entailed.  
> We
> > have a note for the OWL entailment regime that this is the case (for
> > annotations) and that we might want to think about applying  
> different
> > semantics for them, but so far RDF(S) kept us busy and we didn't  
> have
> > the time to think about any solutions for that problem. It is on the
> > list though.
> >
>
> Hm. And again hm:-)
>
> We should probably leave this open and concentrate on the RDFS case  
> now. I must admit
> that I just thought of owl:import without variables, ie, where all  
> these issues do not
> really arise. But you are right, let us leave this open.
>
>
> >> 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...)
> >
> > As I understand it, from named can be used to access graphs in the
> > data set of the query processor. You can do merges into a fresh
> > default graph. Even though this might not be nicest thing in
> > particular for some entailment regimes, this is something that needs
> > to be addressed in the SPARQL query document. The requirement might
> > come from entailment regimes, but entailment regimes are based on
> > SPARQL and if SPARQL does not define it, then we cannot use it. I
> > personally do not want to raise an issue and a request for that, but
> > if others feel like doing it...
> >
>
> I must say I am  a little bit mixed up here, maybe you can help...  
> We discussed the
> issues of restricting entailements specific graphs when those graphs  
> are defined through
> the named graph mechanism of sparql. But I am now messed up on how  
> the FROM NAMED and
> the GRAPH statements would exactly influence entailement, ie when is  
> anything
> restricted. Could you try to summarize this for a better  
> understanding? Maybe this is
> where my confusion comes from... but I am lost a bit:-(
>
> >
> [snip]
> >
> >> 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?
> >
> > Question to the SPARQL implementors/experts. Can I specify my RDF  
> data
> > in turtle and query that in accordance with the spec? If not in
> > accordance with the spec, do systems support turtle input?
> > If yes, then I cannot see, why not functional or manchester syntax.
> > This is obviously not normative. Any system might reject non-RDF-XML
> > input, but many systems might happily take it.
> > If not even turtle is allowed, are there any plans for doing that as
> > an optional syntax? If not, I guess we have to live with RDF XML.  
> That
> > would probably be the end for RIF though, for OWL RDF ML is  
> normative
> > and any conformant system must support it anyway, so it is not as  
> bad
> > for OWL.
> >
>
> Hm (again:-). Yes, you are actually right, I am not sure the spec  
> says anything. My
> impression is that the spec is silent at that point and a URI to a  
> graph amy refer to
> any format that the processor understands. If that is so, we may not  
> have a problem with
> OWL if the processor understands non RDF/XML formats. Maybe it is  
> worth to add this to a
> possible service descriptions, though.
>
> But it is certainly a problem with RIF. Indeed, turtle may not be a  
> standard format but
> it is an RDF serialization syntax. In this sense, both the OWL 2  
> functional syntax and
> the M'ter syntax can be considered as an RDF serialization syntax,  
> because they can be
> converted, in a standard way, to RDF. But an RIF rule set _cannot_:-(
>
> Thanks
>
> Ivan
>
> >> I would expect we should be able to do that, but that might  
> affect the query
> >> language specification.
> >
> > Again, that is up to the general SPARQL/Query spec and however  
> want to
> > raise an issue for that can do so.
> >
> > Birte
> >
> >> 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
> >>
> >
> >
> >
> > --
> > Dr. Birte Glimm, Room 306
> > Computing Laboratory
> > Parks Road
> > Oxford
> > OX1 3QD
> > United Kingdom
> > +44 (0)1865 283529
> >
>
>
> --
> Ivan Herman, W3C Semantic Web Activity Lead
> URL: http://www.w3.org/People/Ivan/
> FOAF: http://www.ivan-herman.net/foaf.rdf
>
Received on Friday, 9 October 2009 07:00:04 GMT

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