[Semediawiki-user] Fw: SparqlExtension 0.7 - querying external endpoints

[Alfredas C. <laf...@ym...>]

----- Forwarded Message ----
From: Alfredas Chm <laf...@ym...>
To: Laurent Alquier <la...@al...>
Cc: sem...@li...; 
sem...@li...
Sent: Mon, September 13, 2010 1:20:27 PM
Subject: SparqlExtension 0.7  - querying external endpoints


Hi Laurent,

as for the querying external endpoints - I have explicitly removed the multiple 
endpoint definitions from the extension. So the query 


{{#sparql: 
select * where { ?x ?y ?z}
| endpoint=dbpedia
}}

will not work.

I decided to follow the SPARQL specification/philospohy on federated queries. So 
the previous query can be replaced by:

{{#sparql: 
select * where { 
   service <http://dbpedia.org/sparql> {
      ?x ?y ?z
   }
}
}}

Please note that the behavior of the two queries is different if you are doing 
aggregation as it is done on the "client"/local endpoint. And different 
endpoints have limits on the number of results (eg dpbedia.org has 1000). 

For example:
1) querying dbpedia.org/sparql directly with:

SELECT ?actor (count(?movie) as ?numberOfMovies) WHERE {
?actor rdf:type <http://dbpedia.org/class/yago/AmericanFilmActors> . 
?movie <http://dbpedia.org/ontology/starring> ?actor . 
} group by ?actor order by desc(?numberOfMovies) limit 10

...would produce a set of results different than...

2) ...querying via local endpoint (federated query):

SELECT ?actor (count(?movie) as ?numberOfMovies) WHERE {
   service <http://dbpedia.org/sparql> {
      ?actor rdf:type <http://dbpedia.org/class/yago/AmericanFilmActors> . 
      ?movie <http://dbpedia.org/ontology/starring> ?actor . 
   }
} group by ?actor order by desc(?numberOfMovies) limit 10

...which is the same query. But as aggregation is done locally, it is done only 
on the 1000 results that you are limited to querying dbpedia.

This is the current behavior of sparql  implementation and the resulting 
behavior of the sparqlextension. I am still considering different ways of 
querying the external endpoints. Hopefully I can get some clarification from the 
SPARQL people before the next release of the extension.

Alfredas






________________________________
From: Laurent Alquier <la...@al...>
To: Alfredas Chm <laf...@ym...>
Sent: Fri, September 10, 2010 10:16:42 PM
Subject: Re: [SMW-devel] SparqlExtension 0.7 released

Thanks

I will compare with the configuration I started and I will let you know if I 
have more questions.
I can't wait to connect to external endpoints from my wiki :)

Regards

- Laurent


On Sep 10, 2010, at 3:51 PM, Alfredas Chm wrote:

Thanks for the tip!
>
>If you need any help setting up joseki + tomcat - let me know. Its not that 
>hard. Basically just download the  webapp (joseki.war) and drop it in the 
>webapps folder.
>Here's http://test.eeni.tbm.tudelft.nl/extensions/joseki-config.ttl the sample 
>config for joseki w/ TDB.
>
>Alfredas
>
>
>
>
>
________________________________
From: Laurent Alquier <la...@al...>
>To: Alfredas Chm <laf...@ym...>
>Sent: Fri, September 10, 2010 7:20:50 PM
>Subject: Re: [SMW-devel] SparqlExtension 0.7 released
>
>By the way.
>
>On the download page, the manual link points to 0.7 .... but the automated 
>download still points of 0.6,
>
>- Laurent
>
>
>On Fri, Sep 10, 2010 at 12:42 PM, Alfredas Chm <laf...@ym...> wrote:
>
>Dear all,
>>
>>
>>SparqlExtension 0.7 has been released. Some highlights:
>>1) Charts - 9 new charts from Google (see 
>>examples http://enipedia.tudelft.nl/wiki/User:Alfredas/Charts).
>>2) Special page - Special:SparqlExtension (implements Google Visualization  
>>DataSource) .
>>3) Support for Semantic Internal Objects.
>>
>>For more info see http://www.mediawiki.org/wiki/Extension:SparqlExtension.
>>
>>Alfredas
>>
>>
>>
>>
>>
>>------------------------------------------------------------------------------
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>>_______________________________________________
>>Semediawiki-devel mailing list
>>Sem...@li...
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>>
>>
>
>
>-- 
>- Laurent Alquier
>http://www.linfa.net
>
>
>