Drug-Gene Associations and bibliographic information about the relationship

Endpoints: 
Query: 
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX pubmed: <http://bio2rdf.org/pubmed_vocabulary:> PREFIX pharmgkb: <http://bio2rdf.org/pharmgkb_vocabulary:> PREFIX dc: <http://purl.org/dc/terms/> select ?drugname ?genename ?article_title where{ { SERVICE <$endpoint-1$> { ?p <http://www.w3.org/1999/02/22-rdf-syntax-ns#type><http://bio2rdf.org/pharmgkb_vocabulary:gene-drug-Association> . ?p pharmgkb:drug ?drug . ?drug <http://purl.org/dc/terms/title> ?drugname . OPTIONAL { ?p pharmgkb:gene ?gene . ?gene <http://purl.org/dc/terms/title> ?genename . ?p pharmgkb:article ?article . } } } OPTIONAL{ {SERVICE <$endpoint-2$> { ?article dc:title ?article_title . ?article<http://purl.org/dc/terms/identifier>?identifier . } } } } limit ??number
Statement: 

Drug-Gene Associations and bibliographic information about the relationship. Limit $number$