tokens: Extending the Ontology of Adverse Events ( OAE ) he2014oae , ODNAE imports related drugs from the Drug Ontology ( DrON ) hanna2013building with their chemical components defined in the Chemical Entities of Biological Interest ( ChEBI ) ontology hastings2012chebi , drug mechanisms of action from NDF - RTbrown2004va , and biological process in the Gene Ontology ( GO ) ashburner2000gene , and links these classes with semantic relations .