Page 135 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Database Management Systems/Managing Database

Notes 8.1 Normalization

Normalization is typically a refinement process after identifying the entities, identifying their
relationships, and defining the tables required in the database and the columns within each
table. The starting point for the normalization process can be visualized as the universal relation.
This relation contains all the attributes of interest, and is structured so that each tuple in the
relation has single-valued element. Normalization results in the formation of tables that satisfy
certain specified constraints and represent certain normal forms. Normal forms are table
structures with minimum redundancy.
E.F. Codd defined the first, second and third normal forms. A revised version of third normal
form is given by Boyce and Codd, which is known as Boyce-Codd normal form. Fagin defined
the fifth normal form.

The process of splitting a relation to reduce the probability that anomalies will occur is known
as decomposition. The key to going about decomposition is logical and methodical way.
Normalization reduces redundancy-using principle of non-loss decomposition, which is the
reduction of a table to smaller tables without any loss of information.
Normalization is the process of refining the design of relational tables to minimize data
redundancy. Normalization consists of a series of rules that should be employed to make sure
that the table is fully normalized by listing the functional dependencies and decomposing it into
smaller, efficient tables. Normalization eliminates data maintenance anomalies, minimizes
redundancy, and eliminates data inconsistency.

Figure 8.1

Unnormalized Tables

Normalized Tables

Normal Forms

Normalization is based on the concept of normal forms. A table is said to be in a particular
normal form if it satisfies a certain set of constraints defined for that normal form.
These constraints usually apply to the attributes of the table and on the relationships among
them.
There are multiple levels of normal forms, each addresses a specific factor that could result in
reducing data maintenance anomalies.

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