audacity/lib-src/redland/rasqal/tests/sparql/part1/dawg-query-001.rq

# Get name, and optionally the mbox, of each person

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?mbox
WHERE
  { ?person foaf:name ?name .
    OPTIONAL { ?person foaf:mbox ?mbox}
  }