code: def _read_xml_db(self):
          
          try:
              metadata_str = self.db_io.read_metadata_from_uri(
                  self.layer_uri, 'xml')
              root = ElementTree.fromstring(metadata_str)
              return root
          except HashNotFoundError:
              return None
docs: read metadata from an xml string stored in a DB.
  
          :return: the root element of the xml
          :rtype: ElementTree.Element