Question

Is the following type of dependencies allowed in 3NF- ?

A-->B

where A is a proper subset of CK
and    B is proper subset of another CK.

Answer 1

Yes it's in 3NF because 3NF allows those FD's X --> Y in which either :

a) X is a super key, or

b) Y is a prime attribute     //(Y is prime implies X must be prime i.e. Prime ---> Prime)

So, in the given FD, B is a prime attribute. Hence, it's in 3NF

Comments

ya..ryt..thanks.

it should be in 3NF

if any one condition of below is true then it is in 3NF

1. FD is trivial( for x-.y, y is proper subset of x)

2. LHS is super key

3. RHS is prime attribute

here 3rd is true hence it is in 3NF

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 (y)

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can anyone tell me why is non-prime -> prime not allowed in 3NF??getting confused in this...

Answer 2

yes , its in 3Nf but not in bcnf .

Comments

pranay i think sould be in bbcnf also . bcnf says that if a dependecy is fron a-B then a should be the superkey . no constraint is applied on b . so it should be in bcnf also .

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they use the term proper subset .

So proper subset of a CK cant be a super key , that why A cant be a SK for that its not BCNf .

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ok got it . thanks