小编Dav*_*vid的帖子

我是SPARQL的初学者,所以如果你能帮助我会很棒..我有这样的RDF文档:

  @prefix foaf: <http://xmlns.com/foaf/0.1/> .
  @prefix lb:   <http://example.org/lastfm/> .

  lb:bob     foaf:knows      lb:user2, lb:user3, lb:user4 ;
       foaf:age        25 ;
       lb:listenedTo   lb:track1, lb:track2 ;
       lb:topArtist    lb:artist1, lb:artist2 .        

  lb:user2   foaf:knows      lb:user5, lb:user6 ;
       foaf:age        40 ;
       lb:listenedTo   lb:track1, lb:track2, lb:track3 ;  
       lb:topArtist    lb:artist2, lb:artist4 .        

  lb:user3   foaf:knows      lb:user5, lb:bob, lb:user6 ;
       foaf:age        19 ;
       lb:listenedTo   lb:track2, lb:track3, lb:track4 ;
       lb:topArtist    lb:artist2, lb:artist3 .      

  lb:user4   lb:listenedTo   lb:track2, lb:track3, lb:track4 ;
       foaf:age        61 ;
       lb:topArtist    lb:artist3, lb:artist4, lb:artist5 .     

  lb:user5   foaf:knows      lb:user7 ;
       foaf:age …