bnode-duplicator.rq

DELETE {
  ?s ?p1 ?bn .
  ?bn ?p2 ?o .
}
INSERT {
  ?s ?p1 ?nbn .
  ?nbn ?p2 ?o .
}
WHERE {
  {
    SELECT ?bn (count(?s) as ?number)
    WHERE {
      ?s ?p ?bn
      FILTER isBlank(?bn)
    }
    GROUP BY(?bn)
  }
  FILTER (?number > 1)
  {
    {
      ?s ?p1 ?bn .
      BIND (BNODE() as ?nbn)
    }
    ?bn ?p2 ?o 
  }
}

In order to be able to represent a graph as a set of key-value pairs, blank nodes should only occur once in the object position.
This SPARQL construct duplicates the blank nodes, so that they occur only once as object.