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a human actor while performing a given use case. There are two types of scenarios: a normal scenario and an abnormal scenario. A sequence diagram captures the interactions of an actor and objects in your application for a given scenario. |
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Figure 2.4.
The updated problem statement. |
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Figure 2.5.
The updated use-case model. |
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The normal scenario captures the normal interaction between the actor and the system. At the analysis level, the system is represented by the main domain object that is the object affected by the actor's activities. You don't care about forms or buttons or interfaces at this point. These objects will be exposed during the design iteration (or phase). In diagramming a normal scenario, you're asking yourself and your project stakeholders what actions the actor will normally carry out when there are no anomalies or error conditions. |
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A use case can take alternative paths, each of which is still normal. For instance, the use case Open Account could have at least two alternative normal scenarios: Open Savings Account and Open Checking Account. |
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Abnormal scenarios capture use case paths that take into consideration anomalies and error conditions. For instance, an abnormal path for Close Account might be The account being closed does not exist. Also, for the Withdraw Funds use case, you'll have a scenario that deals with the situation in which there are not enough funds to withdraw. |
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