# Get names and mboxes, each of which may be optional.
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT ?name ?mbox
WHERE
{
{ ?person rdf:type foaf:Person } .
OPTIONAL { ?person foaf:name ?name } .
OPTIONAL {?person foaf:mbox ?mbox} .
}