Re: How to write queries using named graphs?

Eric Scott Thu, 31 Oct 2013 07:50:10 -0700

You could try something like this:

 select ?a?b?c?d?e
 where
{
       ?g a :MyKindaGraph.
       graph ?g
       {
         ?r rdf:subject <Mr_X>.
         ?r rdf:predicate <isPresident>.
         ?r rdf:object <CountryZ>.
         ?r saidBy ?a.
         ?r saidOn ?b.
         ?r saidAt ?c.
         ?r confidence ?d.
         ?r comment ?e
       }
}



On 10/31/2013 07:26 AM, Maria Jackson wrote:

Yes I am talking about the same. Is it possible to query over Jena such
that there is a join between two named graphs. I know I can write using
reification in SPARQL using:

  select ?a?b?c?d?e
  where{
        ?r rdf:subject <Mr_X>.
        ?r rdf:predicate <isPresident>.
        ?r rdf:object <CountryZ>.
        ?r saidBy ?a.
        ?r saidOn ?b.
        ?r saidAt ?c.
        ?r confidence ?d.
        ?r comment ?e
   }



But I am not sure as to how can I write this query using named graphs
without knowing the names of the graphs. As i am converting from
reification to named graphs automatically. So the user does not know the
names of the graphs


On Thu, Oct 31, 2013 at 7:50 PM, Joshua TAYLOR <joshuaaa...@gmail.com>wrote:

On Thu, Oct 31, 2013 at 9:47 AM, Maria Jackson
<maria.jackson....@gmail.com> wrote:

I think jena employs named graphs as a way to achieve reification. As

named

graphs can achieve reification by attaching only one statement with named
graphs.

Jena uses named graphs to provide names for RDF graphs as specified in
the SPARQL standards.  It's not about reification, it's about having
more than one graph.  It's not unlike the fact that Wikipedia has a
bunch of articles that can be identified by their URLs;  it's not
about refification, it's about providing different articles and not
having just one big article.

Is it possible to express information of the following form using named
graphs, if yes then can someone please help me write this information

using

named graphs, so that I may import the same into Jena:

      _:a rdf:subject "Mr X".
      _:a rdf:predicate "isPresident".
      _:a rdf:object "countryZ".
      _:a saidBy "Tia".
      _:a saidOn "29 October 2013".
      _:a saidAt "New York".
      _:a confidence 0.9.
      _:a comment "This is just a comment by Tia".

Is it possible to write the corresponding query Jena using named graph
query on the above given data?

You'll need to clarify what you're trying to do here. You can already
store this data in a named (or in an unnamed) RDF graph.  Maybe what
you're talking about doing is having a graph named (e.g.)

     <http://example.org/comment_by_tia>

with the triple

     <MrX> <isPresidentOf> <CountryZ>

and then having some triples around somewhere like

     <http://example.org/comment_by_tia> <saidBy> <Tia>
     <http://example.org/comment_by_tia> <saidOn> "2013-10-29"^^...
     <http://example.org/comment_by_tia> <saidAt> <NewYork>
     <http://example.org/comment_by_tia> <confidence> 0.9
     <http://example.org/comment_by_tia> <comment> "This is just a
comment by Tia"

This would be convenient way to provide a sort of reification,
especially because you could put more than one triple in the named
graph, so the "meta-information" could be describing a collection of
triples.  Is this the sort of thing that you're talking about doing?

//JT
--
Joshua Taylor, http://www.cs.rpi.edu/~tayloj/

Re: How to write queries using named graphs?

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