query: SELECT (wd:Q150320 as ?item) (COUNT(DISTINCT ?item) as ?descendants) WHERE
  {
    SERVICE gas:service
    {
      gas:program gas:gasClass "com.bigdata.rdf.graph.analytics.SSSP" ; gas:in wd:Q150320 ; gas:traversalDirection "Forward" ; gas:out ?item ; gas:maxIterations 1000 ; gas:linkType wdt:P40 .
    }
  }