An essential use case model, often referred to as a business or abstract use case model, models a technology-independent view of your behavioral requirements.

基本用例模型，通常称为商业或抽象用例模型，对行为需求的与技术无关的视图建模。

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There are two concrete use cases: Ticket Payment by Internet and Ticket Payment by Phone. These use cases are variations of the abstract use case called just Ticket Payment.

有两种具体的用例：通过因特网支付票费及通过电话支付票费，这些用例是所谓票额支付抽象用例的变种。

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In this case, we use an abstract class to define the service specification, as shown in Figure 5.

在这种情况下，我们使用一个抽象类来定义服务规范，如图5所示。

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