attempting to tackle ACTION-514

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, 
     - Ω0 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 
     * Ω0, 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 Tuesday, 20 September 2011 09:59:56 UTC