Super key is a set of one or more attribute which can uniquely identify a row in the relational schema while function dependecies can not identify the whole row but the can identify the attributes that are dependent.
For a relation schema R = {A, B, C, D, E} and functional
dependencies F = {CE
D, D
B, C
A} super key for this relational schema can be ACE by using ACE we
can uniquely identify a row but by using a functional dependecies
we can not uniquely identify a row.
Candidate key in the minimal super key or minimal set of attributes that can uniquely identify a row in the schema. Every candidate key is a super key but vice versa is not true.
Given relational schema and its functional dependencies:
R = {A, B, C, D, E, F, G, H, I, J, K, L, M}
F = {A
BCDE, E
FGH, I
J, AI
K, AL
M}
Check all the attributes that are not available on the right side of the functional dependencies. A, I, L are not present on the right side of the functional dependencies. Now find the Attribute Closure of A, I, L.
(A, I, L)+ = {A, I, L}
= {A, B, C, D, E, I, J, K, L, M} ( Using A
BCDE, I
J, AI
K, AL
M)
= {A, B, C, D, E, F, G, H, I, J, K, L, M} ( Using E
FGH)
As (A, I, L)+ give the set of all attribute of relation R. So it is an candidate/super key.
If you're still having any doubt then please feel free to ask in the comment section.
Q2: Explain with example the difference between super keys and functional dependencies in relational databases. Show...
Q2: Explain with example the difference between super keys and functional dependencies in relational databases. Show how to find a key (super/candidate) for the following functional dependencies: ? = {?,?,?,?,?,?,?,?,?,?,?,?,?} ? = {?→????,?→???,?→?,??→?,??→?}
Q3: Given a relational schema R = {A,B,C,D,E,F,G,H,1,J,K} and a set of functional dependencies F {A B C D E, E F G H I J,AI →K} and a key(R) = AI = 1. Is R in BCNF? If yes, justify your answer [5 points] 2. If no, explain why and decompose R for two levels only [10 points] 3. Check whether the decomposition in step 2 dependency preserved or not [5 points]
Write the complete proof.
Consider the relational schemas given below and the respective sets of functional dependencies valid in the schemas For each one of the relational schemas, determine the highest normal form, which is valid for a schema. Justify your answer If a schema is not in BCNF, then decompose it into a minimum number of schemas so that each one of them is in BCNF. Justify your answers. Justification must include the derivations of minimal keys from the...
Hi,
This is relational databases question
I'm struggling with this homework question. Trying to better
understand what's being asked. Could you please explain your
answer. Many thanks
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Language: SQL - Normalization and Functional
Dependencies
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