Operation messages

Operation messages are used to allow the workflow to send an operation request to the container and for the container to provide the workflow with the result of that operation.

The general pattern is that the workflow sends an operation request to the container via the message channel. If the container understands the request and determines that it should be fulfillable, it acknowledges the request, and will then perform the necessary steps of the operation. Once the operation is completed (or has failed for any reason not foreseen before sending the ACK), the container will send an operation result message back to the workflow.

Some operations are long running and do not provide a single result. For those, the flow is more complicated. Such operations have separate start, stop and result messages. The CUWO must first send the startXXX-message, which will be replied to by either an error or acknowledgement. If acknowledged, the system then starts sending result messages. If the CUWO does not need any more results, it must send the stopXXX-message, which will also be replied to by either an error or an acknowledgement. If acknowledged, the system will not send any further results.

The following diagram shows the “happy path” assuming there are no errors: