The UML sequence Diagram view presents a sequence of causal dependent events, where events are defined as method entries and exits, as well as outbound calls and return calls (see Figure 20).

UML Sequence Diagram视图中存在一系列的因果依赖事件，这些事件定义为方法实体和出口，也包括外部调用和返回调用(见图20)。

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