Make SPARQL Basic Federated Query extension work

[d2rq]

Make SPARQL Basic Federated Query extension work

[cygri]

For v0.8 we should:

• use latest ARQ
• test that SERVICE works and can invoke remote endpoints
• add something in the documentation about how to enable and use this

[cygri]

After fixing 7db6289, SERVICE now seems to work. I'll leave it out of the documentation for now since it's a standard SPARQL feature, so shouldn't really require special explanation at this point.

Created issue #15 for the actual use of the SERVICE keyword for selecting between multiple local databases.

[snowdenj]

I have tested this successfully. The following statement was used:

PREFIX immsch: http://server:8380/immsch/resource/
SELECT DISTINCT ?s ?study ?organ
WHERE
{
?s1 a sgenie:ImmSample .
?s1 sgenie:name ?sampleName .
?s1 sgenie:study ?study .
SERVICE http://server:8380/immsch/sparql
{
?s a immsch:Sample .
?s immsch:id ?sampleName .
?s immsch:organName ?organ .
}
}

I ran this from a D2RQ 0.8 endpoint with the service call against a D2RQ 0.7 server endpoint. This generated output that returned data on the concept from both endpoints as expected.