Certain data elements or domains either by themselves or in combination are critical to the understanding of an entire record or entity.

某些数据元素或域本身或它们的组合对于理解整个记录或实体非常关键。

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However, in many cases, an entity of importance is a subset of a record, or spans several tables and requires data to be joined through a common key.

但是，在很多情况下，重要的实体是一个记录的一个子集，或者跨多个表，需要通过公共键链接数据。

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This is done to more accurately represent the fact that the instantiated entity class maps to a single record of data.

这样可以更准确地表示实例化的实体类映射到单个数据记录的事实。

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