However, none of their datasets contained the ''multi-function'' compounds that belong to two or more metabolic pathway classes. Since these authors were only focused on addressing the singlelabel classification problem, their methods could not be used to deal with the ''multi-function'' compounds. Actually, according to KEGG [14] , among all the compounds with functional annotations, the ''multi-function'' compounds occupy about 8%. Particularly, these multi-function compounds may play some unique role intriguing to both basic research and drug development and hence are worthy of our special attention.