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Re: attempting to tackle ACTION-514

From: Carlos Buil Aranda <cbuil@fi.upm.es>
Date: Mon, 26 Sep 2011 17:23:53 -0300
Message-ID: <CABdcz9Gm-s18OyXaBhxoT1akr9Ew-DzpMfLT_+JK5BLoR+a7ag@mail.gmail.com>
To: Axel Polleres <axel.polleres@deri.org>
Cc: Gregory Williams <greg@evilfunhouse.com>, SPARQL Working Group <public-rdf-dawg@w3.org>
Hi Axel and sorry for this late reply.

during all the emails between Greg and me I've been trying to fix the
problems that Greg saw in the document. His main concern was in the SERVICE
VAR section, in which the algorithm was evaluated using a bottom up
approach. Using that approach it was not possible to assure that a variable
was bound or not. So me marked the section as informative, not providing the
definition section. Apart from that, the other main issue remaining was the
one aboutthe IRI that you answered before.

Regarding the algorithm in section 3.1 it comes from section 18.2.2.5 in the
main query documtent, there is just a new case which is SERVICE.

Regarding what "the set of variables in-scope in pattern P" means, that
means the variables that are in pattern P which is evaluated inside the
SERVICE. These are the variables which will be returned as a Select vars is
done.

I uploaded the changes you suggested to the CVS.

Carlos


2011/9/20 Axel Polleres <axel.polleres@deri.org>

> Carlos, Greg,
>
>
> I had another look on Greg's comments on Fed-Query as per the thread
> starting at
>
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2011JulSep/0007.html
> going upto:
>
>
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2011JulSep/0035.html
> and
>
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2011JulSep/0165.html
>
> Admittedly, I am a bit confused now (probably just because I haven't
> tackled that earlier and seem to
> have difficulties recunstructing the "history" here)... when I look at
> section 3.1 in the current incarnation of
>   http://www.w3.org/2009/sparql/docs/fed/service
> it seems, some of the things referred to in the mail thread seem to be
> lost... Am I missing something? Looking at the right version?
>
> Particularly, as for
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2011JulSep/0035.html,
> I am not sure anymore whether all that is referred to
> in this email is still in the current draft... Can you summarize/explain
> again in one mail what is the exact remaining issue? For me,
> the "algorithm" in section 3.1 is in its current state quite confusing and
> not really clear.
>
> As for Section 3.2 and the comment in
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2011JulSep/0165.html
>
> > "The evaluation of Service is defined in terms of the SPARQL Results
> [RESULTS] returned
> > by a SPARQL Protocol [SPROT] execution of the nested graph pattern"
> >
> > The "RESULTS" link is to the XML Results document. Can it be defined also
> in terms of the (new) JSON Results document?
>
> Well, I think this is anyways a bit tricky.
> eval() is the evaluation of an algebra expression with respect to an active
> graph... so, it is supposed to return a
> multiset of solution mappings, whereas this sentence seems to suggest that
> we are talking about an XML results document here. Also I find the
>  if IRI
> in the definition a bit strange
> ... I suggest to let go of the pseudo-algorithm for "Definition: Evaluation
> of a Service Pattern" in Section 3.2
> and just write it in more natural language:
>
> -------------------------------
> The evaluation of Service is defined in terms of the multiset of solutions
> corresponding to the result returned by a SPARQL Protocol [SPROT]
> execution of the nested graph pattern against a SPARQL endpoint:
>
>  Definition: Evaluation of a Service Pattern
>
>  Let
>     - iri be an IRI,
>     - vars be the set of variables in-scope in pattern P,
>     - 0 the solution set with one empty solution, and
>     - SilentOp be a boolean variable to indicate that SERVICE execution
> should ignore errors when true.
>
>  Then:
>    eval(D(G), Service(IRI,P,SilentOp)) = Invocation( iri, vars, P, SilentOp
> )
>
> where: Invocation(IRI, Vars, P, SilentOp) is
>     * the multiset of solution mappings corresponding to the results of
> executing query
>      SELECT Vars WHERE P against the service endpoint with IRI iri, in case
> of a successful service invocation according to the SPARQL protocol, and
> otherwise
>     * 0, in case SilentOp is true, and otherwise
>     * err
> -------------------------------
>
> What is still not quite clear to me is what "the set of variables in-scope
> in pattern P" exactly means, can you clarify?
>
> Axel
>
>
>
>
Received on Monday, 26 September 2011 20:24:53 GMT

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