Executing federated queries at http://www.sparql.org/sparql.html

[Monika Solanki]

I have been trying to execute this federated query

PREFIX dc: <http://purl.org/dc/terms/>
PREFIX void: <http://rdfs.org/ns/void#>

SELECT DISTINCT *
from <http://xmlns.com/foaf/0.1/> # bogus, not used
WHERE {
SERVICE <http://void.rkbexplorer.com/sparql>
{
 ?dataset a void:Dataset.
  ?dataset dc:title ?title.
}
SERVICE <http://semantic.ckan.net/snorql>
{
 ?dataset a void:Dataset.
 ?dataset dc:title ?title.
}
}

 over the endpoint available at

http://www.sparql.org/sparql.html

It does not seem to work. What am I missing?

Thanks,

Monika