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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _read_xml_db(self):
 """ read metadata from an xml string stored in a DB. :return: the root element of the xml :rtype: ElementTree.Element """

        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