Database Design
Google
Web www.mahipalreddy.com

 

I'll refer to the following tables when explaining some concepts

Tbl_Staff_Branch

Tbl_Staff_Branch

Tbl_Staff

Tbl_Staff

Tbl_Branch

Tbl_Branch

What are update Anomalies

The Problems resulting from data redundancy in an un-normalized database table are collectively known as update anomalies. So any database insertion, deletion or modification that leaves the database in an inconsistent state is said to have caused an update anomaly. They are classified as

Top

What is Functional Dependency? what are the different types of Functional Dependencies?

Functional Dependencies are fundamental to the process of Normalization Functional Dependency describes the relationship between attributes(columns) in a table.
For example, if A and B are attributes of a table, B is functionally dependent on A, if each value of A is associated with exactly one value of B (so, you can say, 'A functionally determines B').


Functional Dependency diagram

Functional dependency between A and B


Attribute or group of attributes on the left hand side of the arrow of a functional dependency is refered to as 'determinant'

Simple example would be StaffID functionally determines Position in the above tables.


Functional Dependency can be classified as follows:

Top

What is Database Normalization?

Database Normalization is a step wise formal process that allows us to decompose Database Tables in such a way that both Data Redundancy and Update Anomalies(see above for more info on update anomalies) are minimised.
It makes use of Functional Dependencies that exist in a table (relation, more formally) and the primary key or Candidate Keys in analysing the tables.
Three normal forms were initially proposed called First normal Form (1NF), Second normal Form (2NF), and Third normal Form (3NF).
Subsequently R.Boyce and E.F.Codd introduced a stronger definition of 3NF called Boyce-Codd Normal Form(BCNF).
With the exception of 1NF, all these normal forms are based on Functional dependencies among the attributes of a table. Higher normal forms that go beyond BCNF were introduced later such as Fourth Normal Form (4NF) and Fifth Normal Form (5NF). However these later normal forms deal with situations that are very rare.

 

Normalization diagram

Normalization Process

 

Top

www.mahipalreddy.com
Terms and Conditions of Use
Copyright 2004 - 2006 Mahipal Padigela. All rights reserved.