query: ##defaultView:BubbleChart
  #Sources used as references on Wikidata
  SELECT ?source ?sourceLabel (COUNT(?source) AS ?count)
  WHERE
  {
      ?item wdt:P248 ?source .
      SERVICE wikibase:label {
          bd:serviceParam wikibase:language "en" .
      }
  }
  GROUP BY ?source ?sourceLabel
  ORDER BY DESC(?count)