Note that there is no strict rule about writing all details of all steps or a need to use all the elements of a use case. For example, the steps can be written as a continuous paragraph. Hence, there are many styles for writing use cases. UML is not very specific about the text contents of a use case. Limit use cases for modeling behaviors that involve an external actor.
You are recommended to follow the latter view (i.e. For example, they argue that view daily report should be the use case and generate daily report is not to be shown in the use case diagram because it is simply something the system has to do to support the view daily report use case. However, others argue that only use cases providing value to an external user/system should be shown in the use case diagram. The diagram below can be used to indicate that the system generates daily reports at midnight. Note the direction of the arrow is from the extension to the use case it extends and the arrow uses a dashed line. In use case diagrams you can use the > arrows to show extensions. That is, the MSS should give us a complete usage scenario.Īlso note that it is not useful to mention events such as power failures or system crashes as extensions because the system cannot function beyond such catastrophic failures. When separating extensions from the MSS, keep in mind that the MSS should be self-contained. Note that the numbering style is not a universal rule but a widely used convention. OBS informs the User of the cancellation. At any time, 120 seconds lapse without any input from the User. OBS requests to confirm the cancellation. At any time, User chooses to cancel the transfer. User requests to effect the transfer in a future date. Steps 3a1-3a2 are repeated until the data entered are correct.ģb. OBS detects an error in the entered data. OBS transfers the money and displays the new account balance.ģa. OBS requests for details of the transfer.Ħ.
This example adds some extensions to the use case in the previous example.
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