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。
The relation between threshold, weight and matching degree is also discussed. In order to make the querying friendlier, the method to avoid returning null set and corpora is also presented.
研究了权重、阈值和匹配度之间的关系，提出了避免查询结果为空集或全集的方法，使得查询更加人性化。
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