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What is Normalization ?
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Answer Posted / jagan
Normalization is the process of taking data from a problem
and reducing it to a set of relations while ensuring data
integrity and eliminating data redundancy
* Data integrity - all of the data in the database are
consistent, and satisfy all integrity constraints.
* Data redundancy – if data in the database can be found
in two different locations (direct redundancy) or if data
can be calculated from other data items (indirect
redundancy) then the data is said to contain redundancy.
Data should only be stored once and avoid storing data that
can be calculated from other data already held in the
database. During the process of normalization redundancy
must be removed, but not at the expense of breaking data
integrity rules.
If redundancy exists in the database then problems can arise
when the database is in normal operation:
* When data is inserted the data must be duplicated
correctly in all places where there is redundancy. For
instance, if two tables exist for in a database, and both
tables contain the employee name, then creating a new
employee entry requires that both tables be updated with the
employee name.
* When data is modified in the database, if the data
being changed has redundancy, then all versions of the
redundant data must be updated simultaneously. So in the
employee example a change to the employee name must happen
in both tables simultaneously.
The removal of redundancy helps to prevent insertion,
deletion, and update errors, since the data is only
available in one attribute of one table in the database.
The data in the database can be considered to be in one of a
number of `normal forms'. Basically the normal form of the
data indicates how much redundancy is in that data. The
normal forms have a strict ordering:
1. 1st Normal Form
2. 2nd Normal Form
3. 3rd Normal Form
4. BCNF
There are other normal forms, such as 4th and 5th normal
forms. They are rarely utilized in system design and are not
considered further here.
To be in a particular form requires that the data meets the
criteria to also be in all normal forms before that form.
Thus to be in 2nd normal form the data must meet the
criteria for both 2nd normal form and 1st normal form. The
higher the form the more redundancy has been eliminated.
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