def get_ioos_def(self, ident, elem_type, ont):
        """Gets a definition given an identifier and where to search for it"""
        if elem_type == "identifier":
            getter_fn = self.system.get_identifiers_by_name
        elif elem_type == "classifier":
            getter_fn = self.system.get_classifiers_by_name
        else:
            raise ValueError("Unknown element type '{}'".format(elem_type))
        return DescribeSensor.get_named_by_definition(
            getter_fn(ident), urljoin(ont, ident)
        )