In one of my discussions with a customer, there was a query regarding the Human workflow and the flow of control between different activities.
They wanted to know how the BPEL service and Workflow service interacts with
each other. If you see the InitiateTask
operation it is a synchronous operation which calls the workflow service and
passes the payload and task attributes and gets the control back to BPEL
process.
In case of a basic flow the initiate task is executed,
workflow service instance is created and service waits in queue of user to be
approved/rejected or complete an outcome. Where as in BPEL the control returns
after initiateTask invocation, but the next activity is a receive callback from
Workflow service which will only trigger once the user completes his action. So
the BPEL process instance gets dehydrated and waits for action.
In case of designing an advanced flow with multiple
callbacks, the BPEL generates extra code to handle multiple operation updates
that happen from the workflow service. The workflow service will run as an
independent process flow which has java API calls to invoke the callback
operations defined in the TaskService
wsdl to give back control to BPEL after different
task stages. In BPEL, the flow goes into a while loop waiting for a callback from
the workflow service. The Pick activity as shown below will be looking for
onMessage from ->OnTaskCompleted,OnTaskAssigned,OnTaskUpdated
and OnSubTaskUpdated.
- onTaskCompleted — This callback is invoked when the task is completed, expired, withdrawn, or errored.
- onTaskAssigned — This callback is invoked when the task is assigned to a new set of assignees due to the following actions:
- Outcome update
- Skip current assignment
- Override routing slip
- onTaskUpdated — This callback is invoked for any other update to the task that does not fall in the onTaskComplete or onTaskAssigned callback. This includes updates on tasks due to request for information, submit information, escalation, reassign, and so on.
- onSubTaskUpdated — This callback is invoked for any update to a subtask.
To go to
advanced mode, select the Allow task and routing customizations in BPEL
callbacks check box. This will enable
the workflow service to notify the BPEL
process using OnMessage callbacks every time a task is routed to a different
user or when the task status changes
Coming to my customer requirements, they wanted to be
notified incase the task is reassigned for more than 3 times .In case of a
reassign the OnTaskUpdated callback will be invoked and control will get
into the OnTaskUpdated parallel flow where you can add the required
customizations.. So this logic was embedded in this callback flow. After the
flow is completed it again goes back and waits in the while loop till next callback
event is activated from the workflow service.
The figure defines the human workflow process flow
inside the BPEL. The while loop enables the BPEL process instance to wait on
pick activity till the task status gets updated to task completion/expiration/error/stale/withdrawn.
This brings in multiple options for customization within the BPEL based on the
workflow status/updates. This is really good feature using multiple callbacks functionality.
