code: def _get_aggregated_object(self, composite_key):
          
          if composite_key not in self.aggregated_objects:
              self.aggregated_objects[composite_key] = self._init_sink_object(composite_key)
          return self.aggregated_objects[composite_key]
docs: method talks with the map of instances of aggregated objects
              :param composite_key presents tuple, comprising of domain_name and timeperiod