Issue type:

• ➕ Feature request

Description:

Queries in the form of SELECT DISTINCT ?g WHERE { GRAPH ?g { ?s ?p ?o . } } LIMIT 100 do not require full SPARQL execution, but can be optimized to directly check index contents.

The RDF/JS source interface will probably be insufficient to include these optimizations, so we may need an extension in IRdfJsSourceExtended (which we can start implementing in rdf-stores).

Requested in #1552

Related to #1286