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

--
Stas Malyshev
smalyshev@wikimedia.org

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