This paper deals with the semantics of null values in functional dependencies in database theory, and presents three different definitions of FDs in a single relation with marked nulls.

本文研究关系数据库理论中空值在函数依赖中的语义问题，提出了带标志空值的关系中函数依赖的三种定义。

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The theory behind atomic transactions, rollbacks, and other critical database topics are very similar to the issues students study in operating systems.

原子事务、回滚和其它关键的数据库主题背后的理论非常类似于学生在操作系统中学习的问题。

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That approach may sound straightforward in theory, but in practice the vast variety of database structures and possible search terms poses a thorny computational challenge.

这种做法可能在理论上听起来很简捷，但在实践中大量各种不同的数据库结构和可能的搜索词构成了一个棘手的计算挑战。

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In theory, date could be matched against a database kept by the drugmaker.

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If this second theory wins the day, Pfizer will be in the position of trying to use its vast database of Celebrex data to prove that Celebrex is a very special case.

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