Provenance Tracking

G1 (Monica ex:name  Monica Murphy . 
    Monica rdf:type ex:Person) 
G2 (G1 dc:author Chris. 
    G1 dc:date  2/10/2004 ) 
G3 (Monica ex:hasSkill ex:Programming) 
G4 (G3 dc:author Peter. 
    G3 dc:date  2/3/2004 )

SELECT ?x ?y ?z 
WHERE ?a (?x ?y ?z) 
     (?a dc:author Chris)