Preconditions and postconditions are Boolean expressions that act as assertions which are evaluated when entering or leaving a task. A task can contain any number of preconditions and Postconditions.
Preconditions and postconditions help the developer to determine error conditions that can not be handled by the normal workflow. If preconditions or postconditions evaluates to "false", the task is escalated. It may be manually restarted when the error condition has been resolved.
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