Process Engine enables you to specify a correlation field to apply correlation on certain receive tasks, signal start events, and message start events, thereby establishing correlation without specifying or creating a correlation service. In this case, the specified field exists in the receive document and serves as the correlation identifier.

When a correlation service is executed, the expected output is a ProcessCorrelationID that is used as the correlation identifier. Instead of executing a service, the Process Engine retrieves the specified correlation field from the input document and uses it as the correlation identifier.