code: def listDataTiers(self, data_tier_name=""):
          
          if not isinstance(data_tier_name, basestring) :
              dbsExceptionHandler('dbsException-invalid-input',
                                  'data_tier_name given is not valid : %s' % data_tier_name)
          else:
              try:
                  data_tier_name = str(data_tier_name)
              except:
                  dbsExceptionHandler('dbsException-invalid-input',
                                      'data_tier_name given is not valid : %s' % data_tier_name)
          conn = self.dbi.connection()
          try:
              result = self.dataTier.execute(conn, data_tier_name.upper())
              return result
          finally:
              if conn:
                  conn.close()
docs: List data tier(s)