PREFIX data: <http://example.org/foaf/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?mbox ?age ?ppd
FROM  data:aliceFoaf data:bobFoaf
WHERE
  GRAPH data:aliceFoaf
  {
    ( ?alice foaf:mbox <mailto:alice@work.example> )
    ( ?alice foaf:knows ?whom )
    ( ?whom foaf:mbox ?mbox )
    ( ?whom foaf:PersonalProfileDocument ?ppd )
  }
  GRAPH ?ppd
  {
     ( ?w foaf:mbox ?mbox )
     ( ?w foaf:age ?age )
  }