Dear all,
I don't mean to hijack the thread, but for federation purposes, you might be interested in a Triple Pattern Fragments interface [1]. TPF offers lower server cost to reach high availability, at the expense of slower queries and higher bandwidth [2]. This is possible because the client performs most of the query execution.
I noticed the Wikidata SPARQL endpoint has had an excellent track record so far (congratulations on this), so the TPF solution might not be necessary for server cost / availability reasons.
However, TPF is an excellent solution for federated queries. In (yet to be pulbished) experiments, we have verified that the TPF client/server solution performs on par with state-of-the-art federation frameworks based on SPARQL endpoints for many simple and complex queries. Furthermore, there are no security problems etc. ("open proxy"), because all federation is performed by the client.
You can see a couple of example queries here with other datasets: – Works by writers born in Stockholm (VIAF and DBpedia – http://bit.ly/writers-stockholm) – Books by Swedish Nobel prize winners that are in the Harvard Library (VIAF, DBpedia, Harvard – http://bit.ly/swedish-nobel-harvard)
It might be a quick win to set up a TPF interface on top of the existing SPARQL endpoint. If you want any info, don't hesitate to ask.
Best,
Ruben
[1] http://linkeddatafragments.org/in-depth/ [2] http://linkeddatafragments.org/publications/iswc2014.pdf