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Review of Fed-query for LC readiness (ACTION-502)

From: Axel Polleres <axel.polleres@deri.org>
Date: Mon, 1 Aug 2011 14:23:35 +0200
Message-Id: <36AC5475-AB70-4752-9048-881509448878@deri.org>
Cc: Carlos Buil Aranda <cbuil@fi.upm.es>
To: SPARQL Working Group <public-rdf-dawg@w3.org>
I checked the changes in Fed-Query...


On 27 Jul 2011, at 22:04, Carlos Buil Aranda wrote:
> sorry Axel, I overlooked the email. I uploaded a new version with your example. It is much clearer. I added BINDINGS ?s { (:b) (:c) }
> 

Hmmm, I don't see a  BINDINGS query in the current draft... 
here are my detailed comments on Section 2.4 and Section 4:


Section 2.4 
-----------

*
 "This query, on the data above using BINDINGS, has three solutions:

  Query Result:"

--(That query doesn't use BINDINGS...)-->

 "
  This query, on the data above, has three solutions:
 "

*

"
 Next, dispatch a constrained query with the solutions for ?s.

 Query:

  PREFIX foaf:   <http://xmlns.com/foaf/0.1/>
  SELECT ?s ?o
  {
   ?s a foaf:Person
   SERVICE <http://example.org/sparql> {?s foaf:knows ?o }
  } 

 This query, on the data above using BINDINGS, has two solutions:

 [...]
"

--(this is where the BINDINGS query is missing)-->

"
 Next, the query planner, dispatches a constrained query with the these solutions for ?s to the external service endpoint <tt>http://example.org/sparql</tt>, using a BINDINGS clause.

 Query:

  PREFIX : <http://example.org/> 
  PREFIX foaf:   <http://xmlns.com/foaf/0.1/>
  SELECT * {?s foaf:knows ?o } BINDINGS ?s {  (:a) (:b) (:c) }

 This query, has the expected two solutions to the overall query:

 [...]
"


Section 4:
----------

*
"We assume the following data on SPARQL endpoints (or graphs) about various projects in certain subject categories in the local default graph: "

- better like this? ->

"We assume the following data on various projects that contains information about SPARQL endpoints where data about these projects (using the DOAP vocabulary) can be queried from:"

*
"A SERVICE or GRAPH 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:"
-->
A SERVICE or GRAPH clause involving a variable can be executed as a series of separate invocations of SPARQL query services. The results of each invocation are combined using union:"

"is executed sounds like we are prescribing a particular implementation?"

* 
I think this section should - after the algebra is introduced -  get back to the example and show how it is mapped to the algebra.
It seems that this is not trivial to define, particularly, if a query has more than one service request with variables. I would expect some informal text at least explaining something along the lines of "if the patterns can be reordered in a way such that respective bindings can be propagated" or alike. As it stands, I am afraid this section is too vague, even if it is marked as informative.


Axel
Received on Monday, 1 August 2011 12:24:20 GMT

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