RE: SPARQL question: get distinct list of datatypes used for literals



> -----Original Message-----
> From: public-rdf-dawg-comments-request@w3.org [mailto:public-rdf-dawg-
> comments-request@w3.org] On Behalf Of Andreas Langegger
> Sent: 22 August 2008 12:08
> To: Lee Feigenbaum
> Cc: Semantic Web; public-rdf-dawg-comments@w3.org
> Subject: Re: SPARQL question: get distinct list of datatypes used for
> literals
>
>
> hi,
>
> Peter said:
> > It seems like something you should be able to do in basic SPARQL,
> > especially if you are only going to bind ?dt into a CONSTRUCT'ed new
> > graph, and not utilise it further in the WHERE portion
>
>
> Could you give me an example how you would do this? The basis for
> constructed graphs is still the result of an ordinary select, where do
> I get the datatype from? I could fetch it afterwards when getting the
> results, but what I want is a distinct list of data types used, not
> all the values (because of performance, transferring as few results as
> possible).
>
> Lee said:
> > Offhand, I don't know of any SPARQL implementations that do this: at
> > the same time, I don't know of any that don't, other than my own :-D
> > SELECT ?dt {
> >  :s :p ?val .
> >  ?dt a rdfs:Datatype .
> >  FILTER (datatype(?val) = ?dt) .
> > }
>
>
> Andy, would this work with ARQ, if the model in the dataset uses a D-
> entailment capable reasoner?

That depends on the reasoned - if it creates the triple ?dt a rdfs:Datatype then yes.  But that is not directly in the D-entailment rules set as far as I can see.

Pragmatically, this would also work:

SELECT ?dt {
  :s :p ?val .
  GRAPH <mydatatypes.rdf> { ?dt a rdfs:Datatype . }
  FILTER (datatype(?val) = ?dt) .
}

But it means you have to have a graph of potential datatypes (and in the federated case, may end up testing each).  That graph could be local.

        AndyS

>
 At least it would require me to have
> control over the endpoint, which I don't have in general.
>
> Because in my scenario most of the end-points use D2R-server, which
> uses ARQ, I'll try with ARQ select expressions (thanks Lee for the
> link!) and fallback to ordinary (and more expensive) fetching-all-
> values-queries if an Exception occured. It's better than nothing.
>
>
> Thanks,
> Andy
>
> On Aug 21, 2008, at 7:25 PM, Lee Feigenbaum wrote:
>
> > Andreas Langegger wrote:
> >
> >> Hi there,
> >> maybe sb can tell me if this is still possible: I'd like to fetch
> >> all datatype URIs used for object literals in a dataset. There is
> >> the dataset predicate which can be used in filter expressions to
> >> filter literals to a known datatype like xsd:string:
> >> FILTER(datatype(?val) = xsd:string).
> >> But can I bind the value to a variable somehow? With a filter it
> >> can't work (consider FILTER(datatype(?val) = ?dt) where ?val is
> >> bound to literal values and ?dt should give me the type). I could
> >> use property functions, but I'd like to stay with SPARQL specs.
> >> Maybe there is a way to do it I just can't see...
> >> thanks,
> >> AndyL
> >
> > AndyL,
> >
> > There's no way to do this (select functions of values from a graph/
> > dataset) in the SPARQL specification.
> >
> > As you said, various implementations provide extensions that will do
> > this. Please see:
> >
> > http://esw.w3.org/topic/SPARQL/Extensions/Selecting_Expressions

> >
> > Lee
> >
> >> Web of Data Practitioners Days / Oct 22-23 / Vienna
> >> http://www.webofdata.info

> >> ----------------------------------------------------------------------
> >> Dipl.-Ing.(FH) Andreas Langegger
> >> Institute for Applied Knowledge Processing
> >> Johannes Kepler University Linz
> >> A-4040 Linz, Altenberger Straße 69
> >> http://www.langegger.at

>
>
>
> Web of Data Practitioners Days / Oct 22-23 / Vienna
> http://www.webofdata.info

> ----------------------------------------------------------------------
> Dipl.-Ing.(FH) Andreas Langegger
> Institute for Applied Knowledge Processing
> Johannes Kepler University Linz
> A-4040 Linz, Altenberger Straße 69
> http://www.langegger.at
>
>
>
>

Received on Friday, 22 August 2008 13:10:20 UTC