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Federated Query

From: Olivier Corby <Olivier.Corby@sophia.inria.fr>
Date: Wed, 18 May 2011 09:04:00 +0200
Message-ID: <4DD36F60.6030003@sophia.inria.fr>
To: public-rdf-dawg@w3.org
Action 463:  remarks about SPARQL 1.1 Federated Query document for LC.
http://www.w3.org/2009/sparql/docs/fed/service.xml


Best regards,

Olivier



1.1.1 Namespaces

from the SPARQL1.1 Query
->
from the SPARQL 1.1 Query

-- add a " "




1.1.3 Terminology

The following terms are defined in SPARQL Query Language 1.1
->
SPARQL 1.1 Query Language




Solution Mapping  (corresponds to the Concepts and Abstract Syntax term 
"RDF URI reference")
->
IRI (corresponds to the Concepts and Abstract Syntax term "RDF URI 
reference")



2.1 Simple query to a remote SPARQL endpoint

the people I know
->
the people we know



and I want to combine
->
and we want to combine




2.2 SPARQL query with OPTIONAL to two remote SPARQL endpoints

Data in default graph at service: <http://people.example/sparql>
->
<http://people.example.org/sparql>



Query:
   SERVICE <http://people.example/sparql> {
   ->
   SERVICE <http://people.example.org/sparql> {



2.3 Variable Services

http://projects1.example/SPARQL
->
http://projects1.example.org/SPARQL

same for projects2 and projects2



2.3 Variable Services

This query, on the data above, has four solutions:
->
three solutions



2.4 Boundedness Condition

For example, the SPARQL graph pattern
->
For example, in the SPARQL graph pattern




?Y is not strongly bound
->
add a reference to the definition of strongly bound below




  { ?X :p :o SERVICE ?Y { ?Z :p :o } SERVICE ?X { ?Y :p :o } } The
  ->
  a "." is missing before The




2.5 Service Execution Failure

unbounded
->
unbound




If the 'SILENT' token it is not present
->
If the 'SILENT' token is not present



Data in <http://people.example/sparql> endpoint:
->
http://people.example.org/sparql



2.6 BINDINGS

SPARQL 1.1 Query includes the BINDINGS clause (Section 18.2.5.6 BINDINGS)
->
Section 10.2 BINDINGS




3.1 Definition of SERVICE

Tranform(syntax form):
->
Tranform (syntax form):




  Section 18.2.2.4 Translate Graph
  ->
  Section 18.2.2.5

  (may be not a good idea to duplicate section numbers as they may change)




Let SilentOp := boolean, SERVICE indicating error behavior.
->
Let SilentOp := boolean, indicating SERVICE error behavior.




Example: a SERVICE graph pattern in a series of joins:

... WHERE { { ?s :p1 ?v1 } SERVICE <srvc> {?s :p2 ?v2 } { ?s :p3 ?v2 } }

Join( Service( <srvc>,
BGP( ?s :p1 ?v1 ),
BGP( ?s :p2 ?v2 ), false ),
BGP( ?s :p3 ?v2 ) )

->
BGP( ?s :p1 ?v1 ) should not be inside service



Example: a SERVICE SILENT graph pattern in a series of joins:

same remark as above




Definition: Evaluation of a Service Pattern

vars is the set of variables in pattern P
->
I think that vars should be the variables in-scope in P because they are 
used as "select vars where P"



if IRI is a SPARQL service
   Service(IRI,G,P,SilentOp)) = Invocation( IRI, vars, P, Bindings(G, 
vars), SilentOp )
  ->
   eval(D(G), Service(IRI,G,P,SilentOp)) = Invocation( IRI, vars, P, 
Bindings(G, vars), SilentOp )



The evaluation of graph uses the SPARQL algebra union operator.
->
The evaluation of service



Definition: Strongly bound variable

P = P1 GROUP BY E1 ... n
->
P = P1 GROUP BY E1 ... En




(what I want say here is that it is not possible  to guarantee that a 
variable will be bounded after a SERVICE execution).
->
(It is not possible to guarantee that a variable will be bounded after a 
SERVICE execution).



UNBOUND is not a possible value for a ?Xi in BindingValues.
->
UNBOUND is not a possible value for ?Xi in BindingValues.



  P = GRAPH ?X { P1 } and ?X is strongly bound
->
  P = GRAPH ?X { P1 }



Definition: Service safeness

it hold that
->
it holds that



4.1 Grammar


The formal definition for the SPARQL 1.1 Federated Query grammar is 
provided with the SPARQL 1.1 Query grammar
->
add a "." at the end



It is a syntax error if to use
->
It is considered as a syntax error to use



as the first argument to a
->
as the first argument of a




5 Conformance


  See section 7 Internet Media Type for conformance to the 
application/sparql-query media type.
->
there is no such section 7, should be removed



  SPARQL 1.1 Query Language for RDF
  ->
  SPARQL 1.1 Query Language



6 Security Considerations (Informative)

SPARQL Query 1.1 [SQRY] Section 18
->
SPARQL 1.1 Query [SQRY] Section 21
Received on Wednesday, 18 May 2011 07:04:29 GMT

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