完全函数依赖(Full functional dependency)：在一个关系中，若某个非主属性数据项依赖于全部关键字称之为完全函数依赖。
本文给出了空值环境下的完全函数依赖的弱保持、强保持及部分函数依赖。
The weak and strong holds of Full Functional Dependencies and Part Functional Dependencies under the null values environment are proposed in this paper.
当XML文档出现不完全信息时，XML函数依赖同样对于XML文档的键、规范化和完整性约束的研究具有重要意义。
When XML document comes forth incomplete information, XML functional dependency has also important meaning for the research of key, normal form and integral restriction for XML document.
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