As you mentioned Google Knowledge Graph, it's based on the open Freebase ontology. Google bought the company behind Freebase and the ontology will be no more in March 31, 2015: http://www.freebase.com , http://en.wikipedia.org/wiki/Freebase
A rather sad demise. There is an half-hearted(?) attempt to donate some data to WikiData of Wikipedia. But given the track record of WikiData history and how different the ontology is, it looks like Freebase will go offline forever and used as internal datasource for Google Knowledge Graph.
It would be great if Google would donate the data and the tools to generate Freebase to Archive.org or another open source community, so that they can regenerate the ontology on a monthly interval from its Wikipedia, and various other data sources. Given that Freebase is also what powers Siri, Cortana and Watson, maybe another corporation can help.
A rather sad demise. There is an half-hearted(?) attempt to donate some data to WikiData of Wikipedia. But given the track record of WikiData history and how different the ontology is, it looks like Freebase will go offline forever and used as internal datasource for Google Knowledge Graph.
It would be great if Google would donate the data and the tools to generate Freebase to Archive.org or another open source community, so that they can regenerate the ontology on a monthly interval from its Wikipedia, and various other data sources. Given that Freebase is also what powers Siri, Cortana and Watson, maybe another corporation can help.