- A.若 X→Y，X→Z，则 X→YZ 为 F 所蕴涵
- B.若 X→Y，WY→Z，则 XW→Z 为 F 所蕴涵
- C.若 X→Y，Y→Z 为 F 所蕴涵，则 X→Z 为 F 所蕴涵
- D.若 X→Y，为 F 所蕴涵，且 Z1.jpgU,则入 XZ→YZ 为 F 所蕴涵
正确答案及解析
正确答案
解析
从已知的一些函数依赖，可以推导出另外一些函数依赖，这就需要一系列推理规则。函数依赖的推理规则最早出现在1974年W.W.Armstrong 的论文里，这些规则常被称作“Armstrong 公理”设U 是关系模式R 的属性集，F 是R 上成立的只涉及U 中属性的函数依赖集。函数依赖的推理规则有以下三条：自反律：若属性集Y 包含于属性集X，属性集X 包含于U，则X→Y 在R 上成立。(此处X→Y是平凡函数依赖)增广律：若X→Y 在R 上成立，且属性集Z 包含于属性集U，则XZ→YZ 在R 上成立。传递律：若X→Y 和 Y→Z在R 上成立，则X →Z 在R 上成立。其他的所有函数依赖的推理规则可以使用这三条规则推导出。
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