NORMALIZATION
Normalization is a process
that helps analysts or database designers to design table structures for an
application. The focus of normalization is to attempt to reduce redundant table
data to the very minimum. Through the normalization process, the collection of
data in a single table is replaced, by the same data being distributed over
multiple tables with a specific relationship being setup between the tables. By
this process RDBMS schema designers try their best to reduce table data to the
very minimum.
Having said this, when the
process of normalization is applied to table data and this data is spread
across several associated (i.e. a specific relationship has been established)
tables, it takes a query much longer to run and retrieve user data from the set
of tables.
Hence, often in a commercial
application after 100% normalization is carried out across the master tables
often the table structures are de normalized deliberately to make SQL queries
run faster. This means that in commercial applications there is often a trade off
between redundant table data and the speed of query execution.
Normalization is carried out
for the following reasons:
To structure the data
between tables so that data maintenance is simplified
To allow data retrieval at
optimal speed
To simplify data maintenance
through updates, inserts and deletes
To reduce the need to
restructure tables as new application requirements arise
To improve the quality of
design for an application by rationalization of table data
Normalization is a technique
that:
Decomposes data into two
dimensional tables
Eliminates any relationships
in which table data does fully depend upon the primary key of a record
Eliminates any relationship
that contains transitive dependencies
A description of the three
forms of Normalization is as mentioned below.
First
Normal Form
When a table is decomposed
into two-dimensional tables with all repeating groups of data eliminated, the
table data is said to be in its firs normal form.
The repetitive portion of
data belonging to the record is termed as repeating groups.
Second
Normal Form
A table is said to be in its
second normal form when each record in the table is in the first normal form
and column in the record is fully dependent on its primary key.
Third
Normal Form
Table
data is said to be in third normal format when all transitive dependencies are
removed from this data.
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