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Re: Usage of datasets and graphs in triple store

From: Axel Polleres <axel@polleres.net>
Date: Fri, 16 Mar 2018 01:22:16 -0700
Message-Id: <DF9C121A-7D5D-48BF-A303-91CC56DDBBF0@polleres.net>
Cc: Mikael Pesonen <mikael.pesonen@lingsoft.fi>, "semantic-web@w3.org" <semantic-web@w3.org>
To: Mark Wallace <mark.wallace@semanticarts.com>
FWIW, this behaviour of FROM is definitly NOT standardized across triple stores.
The spec says only
"Each FROM clause contains an IRI that indicates a graph to be used to form the default graph. This does not put the graph in as a named graph.
...
If a query provides more than one FROM clause, providing more than one IRI to indicate the default graph, then the default graph is the RDF merge <http://www.w3.org/TR/rdf-mt/#graphdefs> of the graphs obtained from representations of the resources identified by the given IRIs."

while dereferncing and downloading RDF data from the given IRI is one option, what "obtained from representations of the resource identified by the given IRIs" 
exactly means for a triple store is not defined by the spec and left open to the implementation.

just my two cents,
Axel
--
Dr. Axel Polleres	
url: http://www.polleres.net/  twitter: @AxelPolleres

> On 15.03.2018, at 09:42, Mark Wallace <mark.wallace@semanticarts.com> wrote:
> 
> The FROM clause brings in an RDF graph from a URL, so if the external triple store provides a URL to a data set, then it's possible. 
> 
> For example, the RDF4J triple store exposes an HTTP API to access RDF statements in any of its "repositories", so you could do something like:
> 
>   select * 
>   FROM  <http://localhost:8080/rdf4j-server/repositories/myRepo/statements>   
>   where . . .
> 
> So it's definitely possible.  
> 
> SERVICE would seem more efficient than fetching all of the repository statements if the data set is large. 
> 
> -Mark
> 
> -----Original Message-----
> From: Mikael Pesonen <mikael.pesonen@lingsoft.fi> 
> Sent: Wednesday, March 14, 2018 10:39 AM
> To: semantic-web@w3.org
> Subject: Usage of datasets and graphs in triple store
> 
> 
> Hi,
> 
> what would be good reasons to split data to different graphs and also into different datasets?
> 
> About sparql FROM clause, is it possible to fetch data from external triple store, or is SERVICE method for that only?
> 
> Thank you
> 
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Received on Friday, 16 March 2018 08:22:49 UTC

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