If a specification is loaded into the editor that contains a reference to an icon that cannot be found, a special “broken” icon will render in its place, as depicted in Figure 4.18.
66 CHAPTER 4. THE EDITOR Figure 4.18: A task specifying an icon that the editor cannot locate 4.5.5 Task Indicators Task indicators are mini-icons that appear across the top of a task to provide a visual cue regarding certain settings that have been applied to the task. An example of a task with all three possible indicators is shown in Figure 4.19. Figure 4.19: Task Indicators The three task indicators (left to right in Figure 4.19) are: • Timer : This task has had a timer set (see Section 4.13). • Automated : This task has been set as automated (see Section 4.12). If this automated task also has a codelet specified, it will be filled green (see Section 4.12.1). • Cancellation Set : This task has had a cancellation set defined (see Section 4.6). These task indicators are rendered on top of any icons set for the task. 4.6 Cancellation Sets Cancellation Sets allow you to nominate any number of tasks, conditions and/or flow relations (which, when they join two tasks directly, contain an implicit condition that is not visible on the net) for cancellation, upon the completion of a specified task. That is, once a specified task has completed execution in a workflow instance, all other net elements within that task’s nominated cancellation set (if any) are deactivated. To create a Cancellation Set for a task: 1. First select the task to create the Cancellation Set for. 2. Choose V iew Cancellation Set from the El ements menu, or click the View Cancellation Set toolbar button . The task will fill with a grey colour to indicate that this is the task that ‘owns’ the cancellation set currently on view. Create a new “Purchase Book” specification as shown in Figure 4.20, noting that the “Get Book Details” task has an AND-split and the “Pay” task has an XOR-join. In this example, we are going to purchase a book by placing an order with three different sellers. As soon as the first seller fills the order, we want to cancel the other two orders. To achieve this, we create a cancellation set for each “Order” task that includes the other two “Order” tasks. We will step through creating a cancellation set for the “Order from Amazon” task – the other two are created in a similar manner.
4.6. CANCELLATION SETS 67 Figure 4.20: The Purchase Book specification Select the “Order from Amazon” task and view its Cancellation Set using either method described above. 3. Next, choose a task, condition or flow (and thus an implicit condition) to add to the Cancellation Set. Hold down the shift key to select more than one object for cancellation. Select the “Order from Booktopia” and “Order from Bookfinder” tasks, and the flow relation preced- ing each of them.
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