SPARQL query for Graph Density ratio

graphDensity.rq

 SELECT (?nrEdges/(?nrNodes *(?nrNodes - 1.0)) AS ?graphDensity)
 FROM <graphName>
 WHERE {
  { SELECT (COUNT (*) AS ?nrEdges) (COUNT (DISTINCT ?person) AS ?nrNodes)
    WHERE { ?person <knows> ?anotherPerson . }
   }
 }