Explain normalization.
Explain normalization.
In creating a database, normalization is the
process of organizing it into tables in such a way that the results of using
the database are always unambiguous and as intended. Normalization may have the
effect of duplicating data within the database and often results in the creation
of additional tables. (While normalization tends to increase the duplication of
data, it does not introduce redundancy, which is unnecessary duplication.)
Normalization is typically a refinement process after the initial exercise of
identifying the data objects that should be in the database, identifying their
relationships, and defining the tables required and the columns within each
table.
First normal form (1NF). This is the
"basic" level of normalization and generally corresponds to the
definition of any database, namely:
It contains two-dimensional tables with rows
and columns.
Each column corresponds to a sub-object or an
attribute of the object represented by the entire table.
Each row represents a unique instance of that
sub-object or attribute and must be different in some way from any other row
(that is, no duplicate rows are possible).
All entries in any column must be of the same
kind.
Second normal form (2NF). At this level of
normalization, each column in a table that is not a determiner of the contents
of another column must itself be a function of the other columns in the
table.
Third normal form (3NF). At the second normal
form, modifications are still possible because a change to one row in a table
may affect data that refers to this information from another table.
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