code: def reference_handler(self, iobject, fact, attr_info, add_fact_kargs):
          
  
          logger.debug("XXX Found reference with %s" % attr_info)
  
          if 'idref' in attr_info:
              ref_key = 'idref'
              (namespace, namespace_uri, uid) = self.split_qname(attr_info[ref_key])
          elif fact['attribute'] and fact['attribute'] == 'phase_id':
  
              if fact['term']=='':
                  return True
              else:
                  (namespace, namespace_uri, uid) = self.split_qname(fact['value'])
          elif fact['attribute'] and fact['attribute'] == 'kill_chain_id':
              if fact['term'] == '':
                  return True
              else:
                  (namespace, namespace_uri, uid) = self.split_qname(fact['value'])
  
          timestamp = None
  
          if '@timestamp' in attr_info:
              timestamp = attr_info['@timestamp']
  
          #if not timestamp:
          #    timestamp = self.create_timestamp
  
          (target_mantis_obj, existed) = MantisImporter.create_iobject(
              uid=uid,
              identifier_ns_uri=namespace_uri,
              timestamp=timestamp,
              create_timestamp=self.default_timestamp)
  
          logger.debug("Creation of Placeholder for %s %s returned %s" % (namespace_uri, uid, existed))
          add_fact_kargs['value_iobject_id'] = Identifier.objects.get(uid=uid, namespace__uri=namespace_uri)
  
          return True
docs: Handler for facts that contain a reference to a fact.
  
          As shown below in the handler list, this handler is called
          when a attribute with key '@idref' on the fact's node
          is detected -- this attribute signifies that this fact does not contain
          a value but points to another object. Thus we either retrieve
          the object or, if an object with the given id does not yet exist,
          create a PLACEHOLDER object.
  
          We further create/refer to the fitting fact data type:
          we want the fact data type to express that the fact is
          a reference to an object.