See Wikidata:SPARQL_federation_input
> Complies with the SPARQL 1.1 protocol, "query operation" part, at least to the extent necessary to make federated SERVICE clause work (most SPARQL endpoints do). > Contains data that can be linked to Wikidata - i.e., either contains Wikidata IDs or can be queried by values contained in one of the Wikidata properties. > Has data freely available under license compatible with CC0 (preferred) or other free database license allowing unrestricted reuse. Attribution licenses like CC-BY are ok too. Currently, we do not accept endpoints with reuse restriction clauses like NC/ND.
See also:
- Webinarier
- Riksantikvarieämbetets erfarenheter kring länkade öppna data
- Kungliga bibliotekets arbete med länkade data
- Länkade nobelpris – att producera och konsumera länkade öppna data
picture from at 30 minutes the architecture