聚合允许添加任意数量的扩展，而无需定义子类的所有可能的组合。

Aggregating allows any number of extensions to be added, without the need for defining all possible combinations of subclasses.

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发货信息(SHIPPEDORDER)：这个表包含发货id、客户ID、订购的箱子类型、订购的数量和订购的日期。

SHIPPED item information (SHIPPEDORDER) : This table contains shipping ID, Customer ID, type of box ordered, number ordered, and date ordered.

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