RE: [SKOS, SPARQL, ALL] Closure and SPARQL

I'm not trying to suggest that SPARQL should be more expressive than the languages it was designed for, I am merely trying to suggest it should support or be able to express the possibility to query for the transitive closure of the transitive properties native to the rdf schema: rdfs:subClassOf and rdfs:subPropertyOf.

RDF(s) has some semantics, like rdfs:subClassOf,rdfs:subPropertyOf, rdfs:range and rdfs:domain. 
These can be used to infer information. 
As most KR-systems provide a way of retrieving "asserted" and "inferred" information, it just seems a bit strange that SPARQL has no notion of the inferred and can only query for the asserted information, unless you have an "asserted" graph and an "inferred" graph stored seper.

I'm not saying all implementations of SPARQL should implement the inferred option, but it would be very nice if some implementations would, and have the option to express in the query if the result should contain only the asserted, or also the inferred.
Being able to do so would save a lot of applications a lot of trouble of having to go though maintaining an asserted version and an inferred version if they would like to use SPARQL to query it, because it seems that that is the only option for such an application if they want to use SPARQL and query for the asserted and inferred. And this seems like a lot of overhead if this has to be done over and over again for each application that wants to query both. It seems a lot more natural to have a (or a few) SPARQL implementations that have this option, but if this can not be expressed in the query, then this would lead to "customized" parameters for each of those implementations.
It's like the /*+RULE*/ option in oracle queries: you can optimize the queries all you want for oracle, but you'll have to start all over again if you move to another database.
Almost the same thing here: if I would like an implementation that supports querying for the inferred without having to maintain a second inferred graph, I would have to create a custom version with custom keywords in the SPARQL statement. 
It would be much nicer if there was a standard way to express this in the query and not a 1001 implementation dependant different options to express the same. Since SPARQL is designed to query RDF, and RDF has semantics, it seems like a logical step to include it. 

Christoffel

 

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> -----Original Message-----
> From: Enrico Franconi [mailto:franconi@inf.unibz.it]
> Sent: donderdag 8 december 2005 23:58
> To: Christoffel Dhaen
> Cc: McBride, Brian; Christopher Welty; public-swbp-wg@w3.org; public-swbp-
> wg-request@w3.org
> Subject: Re: [SKOS, SPARQL, ALL] Closure and SPARQL
> 
> On 8 Dec 2005, at 15:09, Christoffel Dhaen wrote:
> > As far as I know, RDF does not allow you to state that a property
> > is transitive, but the RDF schema itself has 2 transitive
> > properties: rdfs:subClassOf and rdfs:subPropertyOf.
> 
> True: these are fixed properties that are by definition transitive.
> But what if you want to ask for a descendant (which is the transitive
> closure of a "child" property) when in the RDF graph yoy have only
> the "child" property (which is not transitive)? This is exacttly the
> classical example calling for a transitive closure operator in the
> query language.
> 
> > I could be horribly wrong here, but one of the use-cases listed is:
> > "2.17 Building Ontology Tools (Semantic Web)"
> > It says: "Some parts of the ontology editor require the transitive
> > closure of the query and other parts do not."
> >
> > Imho, a lot of applications will require the transitive closure of
> > the query.
> 
> Perfectly true. The main problem here is that the existence of a
> transitive closure operatore raises the data complexity of the query
> language beyond SQL (it becomes of the same complexity as datalog).
> 
> > I don't think I said that RDF and OWL express transitive closure,
> > but they do express transitivity.
> 
> This does not help. You want the transitive closure of existing non
> transitive properties (see the example of "child").
> 
> > And indeed, the transitive closure of the transitive properties is
> > what I would expect to find in a query language for RDF.
> 
> Sure, but it ain't easy: you need a full fledged "graph" query
> language (see, e.g., [1]), while I guess that SPARQLl suffers of a
> mixed origin: a bit of SQL/relational data model and a bit of graph
> data model.
> 
> cheers
> --e.
> 
> [1] C Gutierrez, C Hurtado, AO Mendelzon. Foundations of Semantic Web
> Databases. PODS'04
> 
> 
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Received on Friday, 9 December 2005 11:38:14 UTC