关系的闭包运算 Closure Operations
Second, the concept of key is given at the base of element type that takes part in closure operation, and its inference rules are given, which soundness is proved.
2.对参与闭包运算的元素类型定义XML键,给出XML键的推理规则,并证明其正确性。
参考来源 - 不完全信息环境下关于XML文档多值依赖及推理规则的研究·2,447,543篇论文数据，部分数据来源于NoteExpress
根据导集的性质以及闭包运算的定义，得到导集运算的定义。
The definition of derived set calculation can be obtained according to the closure of set and the characteristics of derived set.
另一方面，给出了(h (X)，h)中收敛网的极限通过并、交及闭包运算的表示。
On the other hand, a representation for limit of convergent net in (h (X), h) is given by means of operations of union, intersection and closure.
又类似于从闭包运算出发建立拓扑空间，从而得到了从导集运算出发建立的拓扑空间。
Similar to the building of topological Spaces through the calculation of a closure of set, the topological Spaces can also be built through the derived set calculation.
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