Hello,
We've been working on integrating some external databases in the Query Service endpoint. You can now query in the same time Wikidata and other free knowledge bases. For now, only databases released under the most compatible licenses, such as CC0, are available. Currently available:
* Europeana[1], the huge collection of cultural data, which is entirely available in public domain. * Nomisma.org[2], a collaborative project to provide stable digital representations of numismatic concepts. * Biblioteca Virtual Miguel de Cervantes [3] * Biblioteca Nacional de España [4]
Soon, we plan to also enable querying other databases, with licenses such as CC-BY. We plan to continue add endpoints based on user requests.
The currently available endpoints are listed here: https://query.wikidata.org/copyright.html
The documentation about the feature (which will also be updated when we add more endpoints) is in the Query Service User Manual [5].
Here are some examples to understand how to build such queries: https://www.wikidata.org/wiki/User:Smalyshev_(WMF)/Federation
Thanks a lot for your input! If you have any question or problem, feel free to contact me.
[1] http://labs.europeana.eu/api/linked-open-data-sparql-endpoint [2] http://nomisma.org/ [3] http://data.cervantesvirtual.com/about [4] http://datos.bne.es/sparql?help=intro [5] https://www.mediawiki.org/wiki/Wikidata_query_service/User_Manual#Federation