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Re: SPARQL WG Soliciting Early Reviews of Working Drafts

From: Lee Feigenbaum <lee@thefigtrees.net>
Date: Thu, 01 Jul 2010 21:30:10 -0400
Message-ID: <4C2D4122.9010202@thefigtrees.net>
To: Peter Ansell <ansell.peter@gmail.com>
CC: SPARQL Working Group Comments <public-rdf-dawg-comments@w3.org>
On 7/1/2010 6:44 PM, Peter Ansell wrote:
> The June 1 SPARQL Federation draft [1] doesn't make it clear how
> GRAPHS and FROM/FROM NAMED etc map to, or are omited from, Federated
> queries. It does say "with a query Q and no default-graph-uri or
> named-graph-uri" in section 4.1, but it doesn't make it clear in the
> examples. Is the idea is that you can't use GRAPH/FROM/FROM NAMED when
> you are using SERVICE.
>
> Personally, I would find it much more useful if Federation wasn't
> restricted to the default graph, as any number of endpoints may not
> have any data at all in the default graph which would make them immune
> to federated queries. I wouldn't like to see Federation introduced at
> the expense of graphs.

Hi Peter,

The SERVICE keyword is a way to effectively embed an invocation of the 
SPARQL protocol within a query. The text in 4.1 specifies that the 
remote service should be invoked without any default-graph0uri or 
named-graph-uri parameters. The effect of this is that the remote 
endpoint will use its default RDF dataset -- this default dataset 
consists of a default graph (potentially empty) and zero or more named 
graphs.

You can indeed use a GRAPH clause within SERVICE, and the graph pattern 
within the GRAPH clause will be matched against the remote endpoint's 
named graphs.

Does this explain the situation? If so, does it address your concerns?

> In the BINDINGS syntax, is it 'UNDEF' or 'UNBOUND'. Currently both are
> used but they seem to have the same meaning.
>
> In the section 3 example there is the variable ?human in the bindings
> section, and ?species in the main part of the query. Is ?human
> supposed to provide values for ?species, as it is not used apart from
> that. Seems like a typo where ?human needs to be changed to ?species.

I'll leave these two to be fixed up by the editor in due course.

thanks for the review,
Lee


> Cheers,
>
> Peter
>
> [1] http://www.w3.org/TR/2010/WD-sparql11-federated-query-20100601/
>
Received on Friday, 2 July 2010 01:30:51 GMT

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