[YeGoblynQueenne]

The problem with all this is that Google, Facebook, Linkedin et al are private companies, so their knowledge graphs are, well, theirs.

The idea with the semantic web was that it would be open and it would belong to its users, not to some cabal of giant corporations that would use it to control the internets.

That notion of openness and co-authorship of the knowledge on the web is now as dead as the parrot in the Pythons skit. And we're all much the worse for it- see all the debates about privacy and ownership of personal information and, indeed, metadata.

[M2Ys4U]

IIRC, Common Crawl exposes the semantic data from the sites they crawl. One could build their own knowledge graph (or at least bootstrap one) from that and other available data sources (DBPedia, WikiData etc.)

[PeterisP]

That's not sufficient - the "private" knowledge graphs of e.g. Google aren't "crawlable", they aren't public and don't (solely) rely on the sites. DBPedia+Wikidata+all other open data sources are not sufficient for a good knowledge graph that can be competitive (in terms of coverage, thoroughness, and recency of updates) with what the megacorps can afford to maintain behind closed doors.