query: SELECT DISTINCT ?prefix (COUNT(?item) AS ?count) (SAMPLE(?prop) AS ?prop) (SAMPLE(?item) AS ?item) WHERE {
    ?item wdt:P1320 ?ocid.
     BIND(STRBEFORE(?ocid, "/") AS ?prefix)
     BIND(STRAFTER(?ocid, "/") AS ?suffix)
     OPTIONAL { ?item ?prop ?suffix. }
  }
  GROUP BY ?prefix
  ORDER BY DESC(?count)