def _validate_class(self, cl):
if cl not in self.schema_def.attributes_by_class:<EOL><INDENT>search_string = self._build_search_string(cl)<EOL>err = self.err(<EOL>"<STR_LIT>", self._field_name_from_uri(cl),<EOL>search_string=search_string)<EOL>return ValidationWarning(ValidationResult.ERROR, err['<STR_LIT>'],<EOL>err['<STR_LIT>'], err['<STR_LIT>'])<EOL><DEDENT>
return error if class `cl` is not found in the ontology