Next, you add some base classes for entries, objects, and authors.

接下来，您应该继续为项、对象和作者添加一些基本类。

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The first three classes constitute the base classes of the class hierarchy.

前三个类构成了类层次结构的基类。

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Those base classes have logic for comparing and cloning objects and a lot more.

这些基础类具有比较和克隆对象等逻辑。

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