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Re: still not understanding FROM NAMED

From: Lee Feigenbaum <lee@thefigtrees.net>
Date: Wed, 17 Nov 2010 11:22:07 -0500
Message-ID: <4CE4012F.4060206@thefigtrees.net>
To: Bob DuCharme <bob@snee.com>
CC: Rob Vesse <rav08r@ecs.soton.ac.uk>, public-sparql-dev@w3.org
On 11/17/2010 7:50 AM, Bob DuCharme wrote:
> That makes sense, but if I can do this
>
> SELECT ?classTitle
> WHERE {
> GRAPH <http://example.com/classes/new/201106>
> { ?s <http://example.com/ns/sample#classTitle> ?classTitle } .
> }

Hi Bob,

This query does not specify an RDF dataset, which means it executes 
against whatever your SPARQL endpoint treats as its default data set. 
Some deployments treat this as including all graphs; some treat it as 
none; still others treat it as configurable.

> does FROM NAMED add anything besides the ability to list a few graphs
> and then says GRAPH ?varName so that the graph pattern is applied to
> several graphs?

Right. FROM NAMED explicitly defines the scope of the named graphs for 
the query - the universe of graphs over which a GRAPH ... clause can range.

Slide 13 of http://www.slideshare.net/LeeFeigenbaum/sparql-cheat-sheet 
has a visual explanation of RDF datasets and SPARQL that might (or might 
not!) help.

best,
Lee

>
> thanks,
>
> Bob
>
>
> On 11/17/2010 4:24 AM, Rob Vesse wrote:
>> FROM NAMED specifies Graphs that are used in GRAPH clauses
>>
>> e.g.
>>
>> SELECT * FROM NAMED<http://example.org/myGraph> WHERE { ?s ?p ?o . GRAPH
>> ?g { ?s ?x ?y }}
>>
>> Would first find all triples from the default graph (which may in fact be
>> the union of several graphs) and then the GRAPH part would use Graphs
>> specified in FROM NAMED clauses to match additional triples. At least
>> broadly speaking that is how it should work. Actual implementations tend
>> to vary somewhat.
>>
>> The difference should be that a FROM clause specifies a graph that forms
>> part of the default graph over which the query operates while the FROM
>> NAMED specifies Graphs used only in Graph clauses
>>
>> Rob
>>
>> On Tue, 16 Nov 2010 19:29:23 -0500, Bob DuCharme<bob@snee.com> wrote:
>>> I understand the various examples in the SPARQL spec that use FROM
>>> NAMED, but I still don't completely understand what the FROM NAMED part
>>> does, especially compared with FROM<http://some/uri>.
>>>
>>> http://www.w3.org/TR/2010/WD-sparql11-query-20101014/#namedGraphs says
>>> "A query can supply IRIs for the named graphs in the RDF Dataset using
>>> the FROM NAMED clause." If they're named graphs, don't they already have
>>> IRIs as names? What is FROM NAMED adding here?
>>>
>>> thanks,
>>>
>>> Bob
>
>
Received on Wednesday, 17 November 2010 16:22:47 GMT

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