Count the identifiers per data source and order them from high to low

Statement: 

Count the identifiers per data source and order them from high to low . Limit of number per page $number$ (e.g.100)

Query: 
prefix wp: <http://vocabularies.wikipathways.org/wp#> prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> prefix dcterms: <http://purl.org/dc/terms/> SELECT DISTINCT ?datasource ?identifier (count(*) AS ?numberEntries) WHERE { ?concept dc:source ?datasource . ?concept dc:identifier ?identifier . } GROUP BY ?datasource ?identifier Limit ??number