This case-sensitive code system http://hl7.org/fhir/v3/QueryResponse defines the following codes in a Is-A hierarchy:
| Code | Display | Definition |
| AE | ApplicationError | Query Error. Application Error. |
| NF | No data found | No errors, but no data was found matching the query request specification. |
| OK | Data found | Query reponse data found for 1 or more result sets matching the query request specification. |
| QE | QueryParameterError | QueryError. Problem with input ParmetersError |