Linked Data(sette)

I've a radical feature idea (possible first as an extension in order to experiment?):

I'd like to link to a remote table from a remote database, e.g. with a function "linked_datasette()". So one could do following query:

SELECT foo.id, foo.a, remote_party.b
FROM foo
JOIN linked_datasette("https://parlgov.datasettes.com/parlgov-b42a2f2") AS remote_party 
  ON foo.id=remote_party.id

This is inspired by SPARQL's SERVICE keyword for remote RDF "endpoints".

There's a foundation in the SQL Standard called SQL/MED (https://rhaas.blogspot.com/2011/01/why-sqlmed-is-cool.html ).

And here's an implementation from me in Postgres FDW to connect another Postgres "endpoint": https://pastebin.com/Fz2v64Cz .

The proposal is described in issue #412 through a linked_datasette() SQL example, with SQL/MED and a PostgreSQL FDW implementation as references. Start by defining the extension boundary and remote-table behavior; the work is done when a documented remote join can be demonstrated reliably.