Hi Laurent,

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

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:

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.


From: Laurent Alquier <laurent@alquier.org>
To: Alfredas Chm <lafredas@ymail.com>
Sent: Fri, September 10, 2010 10:16:42 PM
Subject: Re: [SMW-devel] SparqlExtension 0.7 released


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 :)


- 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.


From: Laurent Alquier <laurent@alquier.org>
To: Alfredas Chm <lafredas@ymail.com>
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 <lafredas@ymail.com> 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.


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- Laurent Alquier