给定关系模式R＜U，F>，U={A，B，C，D，E}，F={B→A，D→A，A→E，AC→B}，则R的候选关键字为CD，分解ρ={Rl（ABCE），R2（CD）}（ ）
- A.具有无损连接性，且保持函数依赖
- B.不具有无损连接性，但保持函数依赖
- C.具有无损连接性，但不保持函数依赖
- D.不具有无损连接性，也不保持函数依赖
正确答案及解析
正确答案
解析
CD能推出题中关系式的所有属性，因此R的候选关键字为CD。
判断是否为无损连接，首先进行R1∩R2=C，由于C不能推出R1或者R2中的任何属性值，因此该分解为有损分解。原关系式F中有D→A而分解的Rl（ABCE）中没有D，所以该分解不保持函数依赖。
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