Specifying the Key
To configure Receive Notification, Wait, and Notify activities, you must specify a key that correlates Notify activities with Receive Notification or Wait activities. The key is a string that corresponding activities specify to determine when a Receive Notification or Wait activity should accept data from a Notify activity. The key is similar to event keys used in activities that wait for incoming events (described in Event). The key is a string, but you can use any XPath expression that evaluates to a string when the process instance executes.
Each Notify activity corresponds to exactly one Receive Notification or Wait activity. That is, as a Notify activity executes, the first Receive Notification or Wait activity that matches the Notify’s key can then execute. You can execute many Notify activities with the same key.
You can create one-to-one correspondence between Wait and Notify activities so that exactly one process’ Notify activity corresponds to one other process’ Receive Notification or Wait activity. Or, you can create many-to-one relationships so that many Notify activities’ keys can correspond to the Receive Notification or Wait in one process. A Notify, however, always only corresponds to only one Receive Notification or Wait activity. Therefore, once a Notify executes, the corresponding Receive Notification or Wait activity continues processing.
See Examples of Inter-Process Communication for examples of specifying keys for Wait/Receive Notification/Notify activities.