Message Exchange Patterns

Selective pull feature allows to pull a subset of messages posted on Message Partition Channels (MPC). The initiating Messaging Service Handler (MSH) sends a pull signal to the responding MSH along with a pull criteria using requestSM. The responding MSH uses requestSM parameters to match the messages present in the MPC and sends back the first matching message as a response using requestUM. A Selective pull mechanism is initiated by a business application by providing simple selection item or complex selection item parameters in the service.

Simple selection, complex selection or both are used to pull messages from an MPC.

Following are the two types of selection:

• Simple selection: Use this option to select messages using any of the following parameters: RefToMessageId, ConversationId, AgreementRef, Service, and Action.
• Complex selection: Use this option to select messages using any of the following parameters: From, To, and MessageProperties.

When you want AS4 to play the role of initiating MSH, IBM webMethods B2B uses the mpc and pmodeId input parameters that are passed to constructSubmitInput service to fetch the appropriate TPA and identify the messaging parameters for the transfer.

The parameters specified in the requestSM leg of the TPA are used to generate the pull signal and identify the address of the responding MSH. When the user message is received as a response to the pull signal, IBM webMethods B2B uses the requestUM leg of the TPA to process the user message.

In One-Way/Pull MEP, use the constructSubmitInput service to package the submitted payload(s) as a user message and submit it to an MPC. The service uses the values of the ReceiverID, ReceiverIDType, SenderID, SenderIDType, and pmodeID. If pmodeID is empty, then a tuple of ReceiverID, toRole, SenderID, fromRole, service, action, and agreementRef input parameters to retrieve the appropriate TPA. The values in the TPA are then used to identify the messaging parameters. Instead of transferring the message to the initiating MSH, the IBM webMethods B2B stores the message in the MPC specified in the legs/businessInfo/mpc TPA parameter of the requestUM leg.

When a pull signal is received, AS4 determines which TPA to use to process the pull signal by matching the MPC named in the pull signal with the MPC named in the requestSM leg of each TPA that is configured in IBM webMethods B2B. The matching MPC is used to process the pull signal. AS4 retrieves the user message from the MPC specified in the pull signal and sends it to the initiating MSH. If no MPC is specified in the pull signal, AS4 uses the default MPC to pull the user message.

AS4 uses the IBM webMethods B2B database as the MPC queue. When a user message is queued, the message is stored in IBM webMethods B2B with a UserStatus of QUEUED, and the corresponding bizDocId is cached. When a pull signal is received, the module first retrieves the bizDocId from the cache First In - First Out, and then retrieves the user message that corresponds to this bizDocId from IBM webMethods B2B. The retrieved message is then sent to the initiating MSH.

IMPORTANT When purging the transaction analysis in IBM webMethods B2B, do not delete user messages in the QUEUED state.

When you want AS4 to play the role of initiating MSH, the Two-Way/Sync transfer is initiated by IBM webMethods B2B.

The parameters specified in the requestUM leg of the TPA are used to generate the user message and identify the address of the responding MSH. After IBM webMethods B2B receives a reply, it uses the replyUM leg of the TPA to process the user message.

If IBM webMethods B2B does not receive a response within the time-period defined in AS4 configuration, an error message is generated by the initiating MSH.

When you want AS4 to play the role of responding MSH, use the constructSubmitInput service to submit a reply user message to the corresponding request user message by setting sync flag to true. The refToMessageId of the reply user message should be set to the request user message's MessageId value. AS4 uses the requestUM leg of the TPA to process the request user message and sends the reply to the initiating MSH.