Message Correlation

Message Correlation

Having messages arrive at the correct process instance requires a mechanism to link them to their rightful process instance. This mechanism is called Message Correlation and attaches a unique identifier to every process instance. This identifier is called the business-key. The business-key will get attached to every outgoing message automatically. A message can then be sent back to the organization which initiated the communication and have it arrive at the same process instance that initially sent the message since the returning message will have the same business-key attached.

It is possible that the business-key is insufficient to map messages to the correct process instance. Like when using subprocesses in the BPMN model which all expect messages to be sent to them, not the parent process. To solve this issue, Task resources also come with an Input Parameter called correlation-key. This is a secondary identifier attachable to all messages if they need to arrive at a specific subprocess. The Variables class provides methods to create Targets with a correlation-key value. The value is usually given as a UUID. When using the Process Plugin API's TargetProvider to create targets for messages, its builder offers the option to decide whether a correlation-key should be part of each Target instance. If set, the Task will automatically have a correlation-key set when it is sent to the target.