Database Normalization in DBMS: Keys and Normal Forms, Summaries of Relational Database Management Systems (RDBMS)

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NORMALIZATION IN

DBMS

• GAYATHRI R

Keys in RDBMS:

Full dependency:

• (^) If all attributes of the primary key are required for the identifying value of a non-primary attribute then it is known as Full Dependency.
• (^) When all non-primary attribute are dependent on whole primary key and they cannot be get defined using only partial part of primary key then it is called as Full Dependency. Here the primary key is roll_no+ sub_id. If we want a mark of any student, we require both roll_no and sub_id. We cannot obtain marks based on one attribute from the primary key.

Roll_n

o

Sub_i

d

mark

s

Partial dependency:

• (^) If the value of a non-primary attribute can be defined using part of the primary key then it is called a partial dependency.
• (^) Partial dependency occurs when primary key is formed using more than one attribute.This type of key also called as composite key. For example, sub_id = 131 will have the sub_name = ‘math’ here we required only partial primary key i.e. sub_id. R O L L _ N O S U B _ I D S U B _ N A M E MA R K S 1 121 Science 80 1 131 Math 65 2 131 Math 95

Normalisation:

• (^) Process in which we

organize the given data by

minimizing the redundancy

present in a relation.

• (^) Divides the single table

into smaller tables and

links them using

relationships.

Second Normal Form

(2NF):

A table is said to be in 2NF if both the following conditions hold:

• (^) Table is in 1NF (First normal form)
• (^) No non-prime attribute is dependent on the proper subset of any candidate key of table i.e. no partial dependency. An attribute that is not part of any candidate key is known as non- prime attribute.

Third Normal Form

(3NF):

• (^) In 3NF, the given relation should be 2NF, and no transitivity dependency should exist, i.e., non-prime attributes should not determine non-prime attributes.
• (^) Note: If A->B and B->C are two FDs then A->C is called transitive dependency.

Example contd…

• (^) If a table has no repeated groups, it is in 1NF.
• (^) 2NF(second normal form ) is used to eliminate the partial dependencies present in the database.
• (^) 3NF(third normal form ) is used to eiminate the transitives dependencies present in database.

Boyce Codd Normal Form

(BCNF/3.5NF):

• (^) Every functional dependency X -> Y, X is the super key of the table.