Re: how to specify that in SERVICE VAR how we query all possible sparql endpoints

Dear all,

I have uploaded a new version that contains the changes suggested by Andy.

cheers,

Carlos

2011/7/26 Andy Seaborne <andy.seaborne@epimorphics.com>

>
>
> On 25/07/11 12:35, Carlos Buil Aranda wrote:
>
>> Hello all,
>>
>> I've been working in dividing the Fed extension semantics section in
>> two, one for SERVICE and another one for SERVICE VAR. I just added new
>> semantics definition for SERVICE VAR, but now, in that part I do not
>> know how to specify that when doing SERVICE ?X, ?X may be still not
>> bounded and a query to all possible values may happen. Any idea?
>>
>
> Section 2.3 talks about SERVICE ?var as an optional feature and the
> document has quite a lot of machinary that drfines it (boundedness
> condition, evaluation semantics, strongly bounded variable, service
> safeness).
>
> I'd like to suggest a different approach which is to describe it (sec 2.3 -
> and it's would be marked "Informative"), provide some guidance text as to
> what it might do, and then not mention it in the definition section. The
> guidance text would include some conditions but done in language and not be
> exhaustive.
>
> Put this section after the formal definition (currently sec 3), before
> "conformance".  Section 4 (Grammar) can be removed as it is in the query doc
> already (I thought we'd already decided to do that).
>
> This section could include the structure that it's a loop over the possible
> values of the variable, and the results unioned together.  c.f. GRAPH ?var
>
> Define SILENT to mean it applies to each invocation, so failure of one
> invovation does not fail the entire SERVICE ?var
>
> The determination of the possible values of the variable is the part left
> undefined.
>
> Don't define "Strongly bound variable" or "Service safeness" -- we are
> going to keep it informative and they make it too much like a formal
> definition after all..
>
> Rough idea:
> """
> A SERVICE clause involving a variable is executed as a series of separate
> invocations of SPARQL query services.  The results of each invocation are
> combined using union
>
> <insert something like the defn box "Evaluation of a Service Pattern with
> Variable" here>
>
> The query engine must determine the possible target SPARQL query services.
>
> The exact mechanism for doing this is not defined in this document.
>
> It must be done in a way that is compatible with the rest of the query
> results, such as constraints on variables from other graph pattern matching
> in the query.  Execution order may also be used to determine the list of
> services to to be tried.
> """
>
> I don't think we can include a formal definition and argue it's left open.
>
>        Andy
>
> http://lists.w3.org/Archives/**Public/public-rdf-dawg/**
> 2011JulSep/0051.html<http://lists.w3.org/Archives/Public/public-rdf-dawg/2011JulSep/0051.html>
>
>