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Re: FROM and FROM NAMED: To fetch or not to fetch?

From: Gregory Williams <greg@evilfunhouse.com>
Date: Mon, 18 Jun 2012 22:00:20 -0400
Cc: public-rdf-dawg-comments <public-rdf-dawg-comments@w3.org>
Message-Id: <CDC8F044-826C-4E65-BB33-00986714334C@evilfunhouse.com>
To: David Booth <david@dbooth.org>
On Jun 2, 2012, at 11:42 PM, David Booth wrote:

> When a SPARQL query is issued to a server using the FROM <U> (or FROM
> NAMED <U>) syntax, is the server supposed to fetch that graph from U or
> is it supposed to only look among its existing named graphs for U?
> These sections certainly make it sound like the server is supposed to
> fetch from the URI (or perhaps use a cached version if it is fresh).
> But I just tried this with three different SPARQL servers, and only one
> fetches from the URI.  The others only look among their existing named
> graphs.
> There is a big difference between fetching and not fetching.  As a query
> writer I need to know which behavior is correct.  

Hi David,

(This is a personal, and not a working-group-official, response.)

Beyond what Andy said in his response (regarding dataset construction being implementation specific), the Service Description vocabulary may provides some help in this situation. The sd:DereferencesURIs feature defined in the SD document[1] can be used to indicate that the implementation will dereference URIs used in the query when constructing the dataset.

Based in part on your comment, the working group is currently looking at the wording of that feature with regard to Update operations, but its definition/use should be considered stable regarding Query operations (as it was included based on the way existing implementations work).


[1] http://www.w3.org/TR/sparql11-service-description/#sd-dereferencesuris
Received on Tuesday, 19 June 2012 02:00:45 UTC

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