Modeling message events

Use a message event to represent a point in your process where an incoming message is received or where an outgoing message should be sent.

Incoming messages can originate from a message event in a process, a Web Service that you create, a message that you post to the JMS Listener, or simply by calling a UCA in an IBM® Business Process Manager service. If you want to create Web Services to initiate inbound requests from external systems, see Publishing IBM Business Process Manager Web Services.

If you want to post a message to the JMS Listener, the Event Manager has a defined XML message structure that it must receive from an external system. See Posting a message to IBM Business Process Manager Event Manager for more information about the required message structure.

Outgoing messages can be received by a message event in a process, can be sent to call an external service, or can be received by the Start event in another process or processes. To learn how to configure message events to send messages, see Using intermediate message events to send messages and Using end message events.

You can include the following types of message events in your BPDs:

Table 1. Available types of message events
Event type	Implementation	When to use
Start event	Message configured to receive (Start events can only receive messages)	Use to model the start of a process if you want an incoming message event to kick off the process. A BPD can include more than one Start Message Event. Use as the start event for an event subprocess when you want the event subprocess to be triggered upon receipt of a message.
Intermediate event	Message configured to receive	Use to model a message event received during the running of the activities in a process. Intermediate events can be attached to activities within your BPDs or they can be included in the process flow, connected with sequence lines.
Intermediate event	Message configured to send	Use to model a message event to be sent during the running of the activities in a process. Intermediate events can be included in the process flow, connected with sequence lines.
End event	Message configured to send (End events can only send messages)	Use to model a message event to be sent at an end point in a process.

When you create a message event, you can cut and paste or copy and paste that message event within the same BPD or from one BPD into another BPD.

Before including any type of message event in a BPD, you should be aware of the following:

Messages can be received by any running process that contains one or more message event.
You can configure message events to consume messages. If you do, when a message is delivered to a running process, the message is consumed by the first message event in the BPD that can accept it (as determined by the UCA that is attached to the message event). When a message is consumed, it will not be processed again by that message event, or any other message event in the BPD instance that can accept it, should the execution of the BPD instance loop back and reach the same message event(s). If a new instance of the message is delivered to the process instance, this message is available for consumption again and is accepted by the message event.
Message events can be used to enable roll-forward scenarios in which the same message needs to be passed through multiple steps until it reaches the appropriate step in the process where it is to be consumed. To enable rolling a message forward through multiple message events, enable the Consume Message option only for the last message event in the chain of roll-forward message events. You can also use conditions to further control message consumption.
Occasionally, you may need to set conditions on the processing of incoming messages. If the condition that you specify evaluates to true, the message is accepted and processing continues—otherwise, it is stopped. Because the message condition is evaluated before the message values can be passed to the input variables of the process definition, the message values are passed to the condition in a special namespace, tw.message . If the message condition evaluates to true, the values are passed from the tw.message namespace to the BPD input variables.