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Normalization

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Normalization

Normalization is the process of removing redundant data from

tables in order to improve storage efficiency, data integrity

(accuracy and consistency) and scalability (accomodates

changes).

This improvement is balanced against an increase in

complexity and potential performance losses from the joining

of the normalized tables at query-time.

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Steps in Normalization

Normalization can be accomplished and understood in stages,

each of which corresponds to a normal form.

A normal form is a state of a relation that results from applying

simple rules regarding functional dependencies ( or

relationships between attributes) to that relation.

Below are brief descriptions of the rules in normalization.

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Steps in Normalization

First Normal Form. Any multivalued attributes (also called

repeating groups) have been removed, so there is a single

value (possibly null) at the intersection of each row and column

of the table.

Second Normal Form. Any partial functional dependencies

have been removed.

Third Normal Form. Any transitive dependencies have been

removed.

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Steps in Normalization

Boyce/Codd normal form. Any remaining anomalies

(Deviation) that result from functional dependencies have been

removed.

Fourth normal form. Any multivalued dependencies have been

removed.

Fifth normal form. Any remaining anomalies have been

removed.

We describe and illustrate first through third normal forms only

in this section

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First Normal Form

A Table in which the intersection of every column and record contains

one and only value

Steps to Remove Repeating Groups

Remove the repeating columns from the original unnormalized table.

Create a new table with the primary key of the base table and the repeating

columns.

Add another appropriate column to the primary key, which ensures

uniqueness.

Create a foreign key in the new table to link back to the original

unnormalized table.

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Table Not Satisfying 1 NF

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After 1 NF……..

Branch Number

Address Branch Number Telno

B001 566443

B001 X Street BGL

B001 342342

B002 233444B002 Y Street Chennai

B002 456454

PRIMARY KEY

FOREIGN KEYPRIMARY KEY

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Second Normal Form

A table is in second normal form if the table is in the first

normal form and every non-primary key column is functionally

dependent upon the entire primary key.

No non-primary key column can be functionally dependent on

part of the primary key.

If A and B are 2 columns, B is fully functionally dependent on

A.B is not dependent on any subset of A.

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Second Normal Form

A table in the first normal form will be in second normal form if

any one of the following applies:

The primary key is composed of only one column

No non-keyed columns exist in the table.

Every non-keyed attribute is dependent on all of the columns

contained in the primary key.

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Second Normal Form

Steps to Remove Partial Dependencies

Determine which non-key columns are not dependent upon the

table’s entire primary key.

Remove those columns from the base table. Create a second table

with those non-keyed columns and a copy of the columns from the

primary key that they are dependent upon.

Create a foreign key from the original base table to the new table,

linking to the new primary key.

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Table not in 2 NF…

Staff no Branch No Branch Address

Name Position Hours per week

1 B001 X Street Bgl

Anitha Assistant 16

2 B002 Y StreetChennai

Swetha Assistant 12

1 B002 Y street Chennai

Anitha Assistant 3

2 B001 X Street Bgl

Swetha Assistant 4

Composite primary key

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Values in branch address can be worked out from only branch

number so table not in 2 NF.

Values in name and position columns can be worked out from

only Staff Number so table not in 2 NF.

Solution…We have to remove the fields which depend on the

partial Primary key.

Not in 2 NF…..

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Branch Number

Address Staff Number

Name Position

1 Anitha Assistant

B001 X Street Bgl2 Swetha AssistantB002 Y Street

Chennai

Branch Number Staff Number Hours per week

B001 1 16

B002 2 12

B001 1 4

B002 1 3

Primary keyPrimary key

Primary key

After 2 NF……..

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A table is in third normal form if every non-keyed column is

directly dependent on the primary key, and not dependent on

another non-keyed column.

If the table is in second normal form and all of the “transitive

dependencies” are removed, then every non-keyed column is

said to be “dependent upon the key, the whole key, and

nothing but the key”.

Third Normal Form

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Steps to Remove Transitive Dependencies

Determine which columns are dependent on another non-keyed

column.

Remove those columns from the base table.

Create a second table with those columns and the non-key

columns that they are dependent upon.

Create a foreign key in the original table linking to the primary key

of the new table.

Third Normal Form

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A Table not in 3 NF…

Branch Number

Branch Address

Telno Manager No

Name

B001 X Street Bgl 543342 X001 Sridharan

B002 Ystreet Chennai

645774 X002 Shekar

Primary Key

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Manager name can be queried by Branch number also by

Manager no. So not in 3 NF.

Not in 3NF…..

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Solution: Converting to 3 NF.

Manager Number Name

X001 Sridhar

X002 Shekar

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Solution: Converting to 3 NF.

Branch Number Address Telno Manager Number

B001 X Street Bgl 566434 X001

B002 Y street Chennai 345667 X002

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