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RE: Compiling information from several different triplestores

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Tue, 5 May 2009 13:46:53 +0000
To: Paul Gearon <gearon@ieee.org>, Nicolas Raoul <nicolas.raoul.lists@gmail.com>
CC: "semantic-web@w3.org" <semantic-web@w3.org>
Message-ID: <B6CF1054FDC8B845BF93A6645D19BEA362D156749D@GVW1118EXC.americas.hpqcorp.net>


> -----Original Message-----
> From: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org]
> On Behalf Of Paul Gearon
> Sent: 5 May 2009 13:39
> To: Nicolas Raoul
> Cc: semantic-web@w3.org
> Subject: Re: Compiling information from several different triplestores
> 
> On Tue, May 5, 2009 at 5:33 AM, Nicolas Raoul
> <nicolas.raoul.lists@gmail.com> wrote:
> > Hello all,
> >
> > How can I run a query over several different triplestores ?
> >
> > For instance, I want to get a list of Anthony's friends.
> > Triplestore1 says Jack is Tony's friend.
> > Triplestore2 says Tony sameAs Anthony.
> > What clever mechanism would undestand that Jack is Anthony's friend?
> > Do I have to copy all information from both triplestores my own
> > triplestore, or is there something smarter to do ?
> 
> Mos triplestores will let you use graph URIs that contain CONSTRUCT
> queries on a SPARQL endpoint. This will transfer more information than
> you need, but will often work if the data is not too large. The other
> issue is that the resulting URL is unwieldy:
> 
> For instance:
> 
> PREFIX : <http://example.com/>
> PREFIX owl: <http://www.w3.org/2002/07/owl#>
> 
> SELECT ?friend
> FROM <triplestore1.uri>
> where {
>   ?person :hasFriend ?friend
>   UNION {
>     ?person :hasFriend ?f2
>     GRAPH
> <http://triplestore2/sparql/?query=PREFIX+owl%3A+%3Chttp%3A%2F%2Fwww.w3.

> org%2F2002%2F07%2Fowl%23%3E%0A%0ACONSTRUCT+%7B%3Fx+owl%3AsameAs+%3Fy%7D+
> WHERE+%7B%3Fx+owl%3AsameAs+%3Fy%7D>
> {
>       ?f2 owl:sameAs ?friend
>     }
>   }
> }
> 
> The above query will find local friend statements (?person :hasFriend
> ?friend) and then import the owl:sameAs statements from the foreign
> store to see their alternative URIs. Of course, I made up the URIs for
> the 2 triplestores, but I'm sure you can adjust as necessary.
> 
> I don't know if all triplestores support this, but I believe Jena and
> Sesame do, and I know that Mulgara does.

Jena/ARQ provides a SERVICE extension for dynamic callout to other SPARQL endpoints.

http://jena.sourceforge.net/ARQ/service.html


I played with dynamic graph fetching (so not a SPARQL endpoint):

http://seaborne.blogspot.com/2008/10/walking-web.html



You an use a URL in FROM:

PREFIX : <http://example.com/>
PREFIX owl: <http://www.w3.org/2002/07/owl#>

SELECT ?friend
FROM <triplestore1.uri>
FROM <http://triplestore2/sparql/?query=PREFIX+owl%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F2002%2F07%2Fowl%23%3E%0A%0ACONSTRUCT+%7B%3Fx+owl%3AsameAs+%3Fy%7D+WHERE+%7B%3Fx+owl%3AsameAs+%3Fy%7D>

where {
  ?person :hasFriend ?friend
  UNION { 
    ?person :hasFriend ?f2
    ?f2 owl:sameAs ?friend
    }
  }
}


	Andy

> 
> Regards,
> Paul Gearon

Received on Tuesday, 5 May 2009 13:48:13 GMT

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