Among the papers under DB classification, which paper has the highest number of words cited?
classification refers to class_label; class_label = 'DB';
SELECT T1.paper_id FROM paper AS T1 INNER JOIN content AS T2 ON T1.paper_id = T2.paper_id WHERE T1.class_label = 'DB' GROUP BY T1.paper_id ORDER BY COUNT(T2.word_cited_id) DESC LIMIT 1