ASK — boolean queries

ASK { … } returns true iff the pattern has at least one solution.

What it does

pgrdf.sparql('ASK { ... }') returns a single JSONB row {"ask": true} or {"ask": false}. Internally pgRDF translates to a SELECT EXISTS against the underlying BGP, so the executor short-circuits on the first match.

Why you'd use it

• Application developers — existence checks ("does this entity have any foaf:mbox?") without scanning solutions.
• Data scientists — quick assertions on graph shape during exploration.
• Operators — health-check queries that gate downstream processing.

Example

SELECT * FROM pgrdf.sparql(
  'PREFIX foaf: <http://xmlns.com/foaf/0.1/>
   ASK { ?s a foaf:Person }');
--  → {"ask": true}

SELECT * FROM pgrdf.sparql(
  'ASK { <http://example.com/notreal> ?p ?o }');
--  → {"ask": false}

Tests

• tests/w3c-sparql/12-ask-true/
• tests/w3c-sparql/13-ask-false/
• tests/regression/sql/44-sparql-ask.sql