| Areas | Area information determined by a hotel reservation system.Defines an area determined by the reservation system. |
| Criteria | Hotel search criteria.A collection of single search criterion items. |
 Errors | Standard way to indicate that an error occurred during the processing of an OpenTravel message.A collection of errors that occurred during the processing of a message. |
| POS | Point of Sale (POS) identifies the party or connection channel making the request.Point of Sale (POS) identifies the party or connection channel making the request. |
| Properties | A collection of individual property information. |
| Success | Standard way to indicate successful processing of an OpenTravel message.Returning an empty element of this type indicates the successful processing of an OpenTravel message. This is used in conjunction with the Warning Type to report any warnings or business errors. |
| TPA_Extensions | A placeholder in the schema to allow for additional elements and attributes to be included per Trading Partner Agreement (TPA).Allows extensions to be added to the OpenTravel specification per trading partner agreement. |
| Warnings | Standard way to indicate successful processing of an OpenTravel message, but one in which warnings are generated.Collection of warnings. |
| AltLangID | The alternate language for a customer or message encoded as ISO 639-3. |
| CorrelationID | Allows end-to-end correlation of log messages with the corresponding Web service message throughout the processing of the Web service message. |
| EchoToken | A reference for additional message identification, assigned by the requesting host system. |
| PrimaryLangID | The primary language preference for the message encoded as ISO 639-3. |
| RetransmissionIndicator | When true, indicates the message is being re-sent after a failure. |
| SequenceNmbr | The sequence number of the transaction assigned by the sending system for ordered message processing or message resynchronization. |
| Target | Test or Production target system indicator. |
| TargetName | The name of the Test or Production system. |
| TimeStamp | ISO 8601 encoded timestamp indicating the creation date and time of the message. |
| TransactionIdentifier | Unique identifier to relate all messages within a transaction (e.g. this would be sent in all request and response messages that are part of an on-going transaction). |
| TransactionStatusCode | This indicates where this message falls within a sequence of messages. |
| Version | The OpenTravel message version indicated by a decimal value. |