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RE: draft response for PW1

From: Polleres, Axel <axel.polleres@siemens.com>
Date: Tue, 3 Jul 2012 17:46:22 +0200
To: "cbuil@fi.upm.es" <cbuil@fi.upm.es>, "andy.seaborne@epimorphics.com" <andy.seaborne@epimorphics.com>, "greg@evilfunhouse.com" <greg@evilfunhouse.com>
CC: "public-rdf-dawg@w3.org" <public-rdf-dawg@w3.org>
Message-ID: <9DA51FFE5E84464082D7A089342DEEE8013E038BF065@ATVIES9917WMSX.ww300.siemens.net>
In what form would tyou want to reference reference to the SPARQL protocol?
If it's only an editorial change that clarifies matter, that should be ok, IMO.

Axel


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Dr. Axel Polleres
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________________________________

        From: Carlos Buil Aranda [mailto:cbuil@fi.upm.es]
        Sent: Tuesday, 3 July 2012 4:48 PM
        To: Andy Seaborne; Gregory Williams
        Cc: public-rdf-dawg@w3.org
        Subject: Re: draft response for PW1


        Dear all,

        I updated the response to PW. However and looking at the document, I think that it is a bit underspecify and it should be added a reference to the SPARQL protocol next to the explanation of what the SERVICE keyword does. Would it be possible to add it informally?

        Carlos


        2012/6/29 Andy Seaborne <andy.seaborne@epimorphics.com>


                I wonder if there is a need to specify the dataset.  The point about SERVICE is to send the query to another place, presumably because it has the data and the sender, and their service engine, does not.  This is emphasising the general SPARQL service that reads graphs off the web and queries them.

                Dataset description is used to select graphs from a local pool.  The use of GRAPH maybe enough to allow the sender to select the graphs of interest.  The only case missing is a merge of graphs to be the default graph.

                If an application wants to access a general purpose SPARQL processor, then it uses the the SPARQL protocol - not as part of a query because , after all, SERVICE happens inside a local query execution.  Shipping off a subpart of the query from one SPARQL engine to another seems a minor use case and if we were addressing that, there is a lot of other machinery that we'd want to put in place.

                        Andy


                On 28/06/12 22:11, Gregory Williams wrote:



                        On Jun 28, 2012, at 4:43 PM, Carlos Buil Aranda wrote:



                                Dear all,

                                I attach the draft response for PW-1 http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2012Jun/0007.html <http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2012Jun/0007.html>

                                draft: http://www.w3.org/2009/sparql/wiki/CommentResponse:PW1 <http://www.w3.org/2009/sparql/wiki/CommentResponse:PW1>



                        Hi Carlos,

                        You say: "in the SPARQL 1.1 grammar there is no way for specifying the default dataset to query."

                        Am I simply misunderstanding what you're saying? For query, you specify it with FROM/FROM NAMED.

                        You continue:

                        """
                        In the same way there is no mechanism for specifying named graphs since the SERVICE keyword only provides mechanisms for directing specific pieces of SPARQL queries to an SPARQL endpoint. Thus, you correctly understood the specification.
                        """

                        I've brought this up before, but why can't the dataset for a SERVICE be specified using protocol parameters? i.e.:

                        SERVICE <http://example.com/sparql?default-graph-uri=XXX&named-graph-uri=YYY <http://example.com/sparql?default-graph-uri=XXX&named-graph-uri=YYY> > { ... }

                        Shouldn't this just work? (Assuming implementors have done the legwork to choose between using '?query=' and '&query=' when constructing the service invocation URI.)


                        """
                        The other possibility you point out (to send the default and named datasets defined by the main query) is not allowed: the SERVICE keyword translates the pattern inside into a new query to the remote dataset, using a SELECT * WHERE {...} without specifying the original query datasets. However, inside the SERVICE clause you can use a subquery in which you can specify to which graph direct the query:

                        PREFIX foaf: <http://xmlns.com/foaf/0.1/>
                        SELECT ?name
                        WHERE {
                          SERVICE <http://example.org/sparql> {
                           SELECT * WHERE
                           {
                            GRAPH <http://example.org/graph>
                             { ?person foaf:name ?name ; foaf:mbox ?mbox }
                           }
                          }
                        }
                        """

                        That won't specify the dataset, though. It only specifies the active graph for matching the two triple patterns.  Is that what you are intending to point out?

                        .greg
Received on Tuesday, 3 July 2012 15:47:12 GMT

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