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what is Normalization means..?
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Answer Posted / nitin bisht
NORMALIZATION: The process of structuring data to minimise
duplication and inconsistencies. The process usually
involves breaking down a single table into two or more
tables and defining relationships between those tables.
Normalisation is usually done in stages, with each stage
applying more rigourous rules to the types of information
which can be stored in a table. While full adherence to
normalisation principles increases the efficiency of a
particular database, the process can become so esoteric that
you need a professional to create and understand the table
design. Most people, when creating a database, don't need to
go beyond the third level of normalisation, called third
normal form. And there's no need to know the terminology:
simply applying the principles is sufficient.
The first three levels in normalising a database are:
First Normal Form (1NF): There should be no repeating groups
in a table.
For example, say you have a students table with the
following structure:
student ID
name
date of birth
advisor
advisor's telephone
student
course ID 1
course description 1
course instructor 1
course ID 2
course description 2
course instructor 2
The repeating course fields are in conflict with first
normal form.To fix the problems created by such repeating
fields, you should place the course information in a
separate course table, and then provide a linking field
(most likely student ID) between the students table and the
course table.
Second Normal Form (2NF): No non-key fields may depend on a
portion of the primary key.
For example, say we create a course table with the structure:
student ID
course ID
course description
course instructor
We can create a unique primary key by combining student ID +
course ID (student ID is not unique in itself, as one
student may take multiple courses; similarly, course ID is
not unique in itself as many students may take the same
course; however, each student will only be taking a
particular course once at any one time, so the combination
of student ID + course ID gives us a unique primary key).
Now, in 2NF, no non-key fields (course description, course
instructor) may depend on a portion of the primary key.
That, however, is exactly what we have here: the course
instructor and course description are the same for any
course, regardless of the student taking the course.
To fix this and put the database in second normal form, we
create a third table, so our database structure now looks
like this (with key fields in italics):
Student table
student ID
name
date of birth
advisor
advisor's telephone
Student courses table
student ID
course ID
Courses table
course ID
course description
course instructor
Third Normal From (3FN): No fields may depend on other
non-key fields. In other words, each field in a record
should contain information about the entity that is defined
by the primary key.
In our students table, for example, each field should
provide information about the particular student referred to
by the key field, student ID. That certainly applies to the
student's name and date of birth. But the advisor's name and
telephone doesn't change depending on the student. So, to
put this database in third normal form, we need to place the
advisor's information in a separate table:
Student table
student ID
name
date of birth
advisor ID
Student courses table
student ID
course ID
Courses table
course ID
course description
course instructor
Advisor table
advisor ID
advisor name
advisor telephone
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