Free Keys, ER and normalization lessonsKeys, ER and normalization · Stage 3 · Normal forms · Step 2
BCNF and good decompositions
The strictest everyday normal form, the case where 3NF and BCNF differ, and how to decompose without losing dependencies. About 14 minutes.
In R(A, B, C) with FDs AB → C and C → B, why is the relation in 3NF but not in BCNF?
- AC → B has a non-key left side, but B is prime (it's in the key AB)
- BThere's a transitive dependency through a non-prime attribute
- CA non-prime attribute depends on part of the key
Show the answer
C → B has a non-key left side, but B is prime (it's in the key AB). 3NF allows that; BCNF doesn't.
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