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ChristopherNg
Posts: 17
Posted 14:22 Dec 03, 2016 |

For example we have R(A, B, C, D, E) and R1(A,B,C)

If we are checking if C is a key of R1 and C -> {A,B,C,D}, is C a key of R1 even with the extra value 'D'? Or does C have to generate exactly {A,B,C} to be a key of R1?

hpguo
Posts: 139
Posted 09:26 Dec 05, 2016 |

There is a rule for FD called decomposition rule which says if  A-> BC then  both A->B and A->C hold.

Dr. Guo