Normalization in databases

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document of baabtra –Mentoring Partner
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NORMALIZATION IN DATABASES
Subhin P.V
111subru@gmail.com
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in.linkedin.com/in/Subhin P.V
8129076036

MAIN POINTS DISCUSSED
• What normalization is and what role it plays in the
database design process
• About the normal forms 1NF, 2NF, 3NF and BCNF
• How normal forms can be transformed from lower
normal forms to higher normal forms

ABOUT NORMALIZATION
• Normalization is the process of efficiently
organizing data in a database.
• Two goals of normalization process:
 Eliminating Redundant Data
 Ensuring data dependencies
• The objective is to isolate data so that changes
of a field can be made in just one table and
then propagated through the rest of the
database using the defined relationships.

Normalization Stages
• 1NF
• 2NF
• 3NF
• Boyce-Codd Normal Form (BCNF or 3.5NF)

First Normal Form (1NF)
• The values in each column of a table are
atomic (No multi-value attributes allowed).
• Each table has a primary key: minimal set of
attributes which can uniquely identify a record
• There are no repeating groups: two columns
do not store similar information in the same
table.

Second Normal Form (2NF)
• Meet all the requirements of the first normal
form.
• Remove subsets of data that apply to multiple
rows of a table and place them in separate
tables.
• Create relationships between these new
tables and their predecessors through the use
of foreign keys.

Third Normal Form (3NF)
• Meet all the requirements of the second
normal form.
• Every non-prime attribute of R is non-
transitively dependent (i.e. directly
dependent) on every superkey of R.
• Remove columns that are
not dependent upon the primary key.

Boyce-Codd Normal Form
• Meet all the requirements of the third normal
form.
• Every determinant must be a candidate key.
• Candidate Key:
 Any attribute or a set of attributes together that
has the eligibility to become a primary key.

TRANSFORMATION FROM UNF TO HIGHER
NORMAL FORMS USING AN EXAMPLE
• Example: Institution Having Two departments
– Each Department Has 6 Different Students And Some
Courses
– Each Student in a department can study more than
one Course
– Each course has its course fee.
– Periodically, report is generated that contains
information displayed which can be represented in a
table as shown in next slide.

Problems With The Table
– The table displays data redundancies.
– The table has Multivalued Attributes
– The table entries invite data inconsistencies.
– The data redundancies yield the following anomalies:
• Update anomalies.
• Addition anomalies.
• Deletion anomalies.

Conversion To 1st Normal Form
– ADVANTAGES
• Each table has at least one minimal set of attributes
which can uniquely identify a record
• The values in each column have Single Value
– DISADVANTAGES
• Redundant data across multiple rows of the table is still
there
• Existence of partial and transitive dependencies

The Dependency diagram
– Depicts all dependencies found within given table
structure
– Helpful in getting bird’s-eye view of all
relationships among table’s attributes
– Makes it less likely that will overlook an important
dependency

Conversion to 2nd Normal Form
{Dep No, Dep_name}
{Stud no, Stud_name, Stud_DOB, Stud_age}
{Dep No, Stud No , Course_name, Course_fee}
Department Details:
Course Details: Student Details:

Conversion to 2nd Normal Form
• Advantages
– eliminates redundant data in the table
– It includes no partial dependencies:
– Create separate tables for sets of values that apply
to multiple records
• Disadvantages
– The table contains Transitive Dependencies.
– Some records depend on attributes other than
the table's primary key

Conversion to 3rd Normal Form
Student Details:
Department Details:
Course Details:
Student course:
{Dep No, Dep_name} , {Stud no, Stud_name,Stud_DOB} , {Dep No, Stud No ,
Course name} , {Course_name, Course_fee}

Conversion to 3rd Normal Form
• Advantages:
– No non-key attribute depends transitively on a
candidate key
– All The attributes in a table Depend on a single
primary key

Conversion To BCNF
• A Case where The table is in 3NF but not in
BCNF

Example of BCNF
fd1 clientNo, interviewDate  interviewTime, staffNo, roomNo (Primary Key)
fd2 staffNo, interviewDate, interviewTime clientNo (Candidate key)
fd3 roomNo, interviewDate, interviewTime  clientNo, staffNo (Candidate key)
fd4 staffNo, interviewDate  roomNo (not a candidate key)
As a consequece the ClientInterview relation may suffer from update anomalies.
For example, two tuples have to be updated if the roomNo need be changed for staffNo
SG5 on the 13-May-02.
ClientNo interviewDate interviewTime staffNo roomNo
CR76 13-May-02 10.30 SG5 G101
CR76 13-May-02 12.00 SG5 G101
CR74 13-May-02 12.00 SG37 G102
CR56 1-Jul-02 10.30 SG5 G102
ClientInterview

Example of BCNF(2)
To transform the ClientInterview relation to BCNF, we must remove the violating
functional dependency by creating two new relations called Interview and SatffRoom as
shown below,
Interview (clientNo, interviewDate, interviewTime, staffNo)
StaffRoom(staffNo, interviewDate, roomNo)
ClientNo interviewDate interviewTime staffNo
CR76 13-May-02 10.30 SG5
CR76 13-May-02 12.00 SG5
CR74 13-May-02 12.00 SG37
CR56 1-Jul-02 10.30 SG5
staffNo interviewDate roomNo
SG5 13-May-02 G101
SG37 13-May-02 G102
SG5 1-Jul-02 G102
Interview
StaffRoom

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