Normalization is an important topic to crack Gate . Experts at GATE – prepladder shares 5 quick tips to solve questions on normalization.
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For analyzing relations based on their primary key and functional dependencies, Normailization is used. Normalization is often performed as a series of tests on a relation to determine whether it satisfies or violates the requirements of a given normal form.
5 quick Tips to solve Questions on Normalization
#Tip1
1NF =>entry should have at most 1 single value, no repeating group,no 2 rows should be same
#Tip2
2NF => it is related with partial dependencies. A relation is in 2 NF when every non-key attributes are dependent on the candidate key
#Tip3
3NF => now this talks about transitive dependencies. It exists when A-->B-->C and not A-->C.In 3NF there should no A->C if A->B and B->C.
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#Tip4
Boyce-Codd Normal Form (BCNF) => checks about determinant. Left side of determined is called determinant. It makes sure all determinants are candidate keys.
#Tip5
4NF => Deals with multi-valued dependencies , X ->> Y means for each value of X, we can have more than one value of Y. It prevents nontrival MVD’s. For 5NF , A relation is in 5 NF if further cannot be non-loss decomposed
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Here is process of normalization.
Solved Examples From GATE
Q1. Consider the following implications relating to functional and multivalued dependencies given below, which may or may not be correct.
- If A ->> B and A ->> C, then A -> BC
- If A -> B and A -> C then A ->> BC
- If A ->> BC and A -> B and A ->C
- If A -> BC and A -> B and A ->> C
Exactly how many of the above implications are valid?
A) 0 (B) 1 (C) 2 (D) 3
Soln. Answer is C
In DBMS, we can see that
If A ->-> B and A->-> C then A -> BC
And A ->-> BC then A ->-> BC
Hence, answer is (c)
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Q2. Examine the table shown below.
branchNo |
branchAddress |
telNos |
B001 |
8 Jefferson Way, Portland, OR 97201 |
503-555-3618, 503-555-6534 |
B002 |
City Centre Plaza, Seattle, WA 98122 |
206-555- 6756, 206-555 -8836 |
B003 |
14 – 8^{th }Avenue, New York, NY 10012 |
212 -371 – 3000 |
B004 |
16 – 14^{th} Avenue, Seattle, WA 98128 |
206 – 555 – 3131, 206 – 555 – 4112 |
- Why is this table not in I NF?
- Describe and illustrate the process of normalizing the data shown in this table to third normal form (3NF)
Soln.
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