Work Item Life Cycle
Internally, every component can be in one of four states: nonstarted, processing, complete, and cancelled. Only the complete state is visible outside a component.
- The nonstarted state indicates that the component has not yet received a token and thus has not yet started task execution.
- The processing state means that the component task is in progress.
- The complete state indicates that the component has completed its task and sent the output token to its successors.
- The cancelled state is an abnormal state that a component enters if it is unable to complete its task or has been ordered by its container to abort the task. The latter occurs when some other component inside a workflow has been cancelled or the workflow engine received a message to do so.
A component completes its task when it terminates the task in a normal condition; the meaning of normal depends on the component. A terminated task could have succeeded in performing its job or not, but in any case the component can be cancelled. A workflow cannot be cancelled after it has completed the task, because it ceases to exist when it communicates its completion to the workflow engine. Figure 4 summarizes the mechanism represented as a state machine in Unified Modeling Language (UML) notation.
When a component cancels, it has to undo anything that may affect the external world, such as directory operations or e-mails. Cancellation ensures that the whole workflow will be cancelled and that all work items are cancelled in the reverse order of their execution.