@Ventronik sparql could be useful. Gnome Tracker is for the desktop but there are possibly other projects for remote data.
"If a majority of apps store data with libtracker-sparql, the shell could use libtracker-sparql to query these databases directly and save the overhead of spawning each app. The big advantage of the federated approach, though, is that search providers can store data in the most suitable method for that data." - https://samthursfield.wordpress.com/tag/tracker/