Database Normalization Vocabulary

Question

There is lot or material on Database Normalization available on SC and the Web. However, I still seem to lack on very definite reasons on explaining normalization.

For example, for a simple design such as a table Item with a Type field, it makes sense to have the Type as a separate table. The reason I forwarded for that was if in future any need arose to add properties to the Type, it would be much easier with a separate table already existing.

Are there more reasons which can be shown to be obvious ?

Answer 1

This article says it better than I can:

There are two goals of the normalization process: eliminating redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.

Answer 2

Normalization is the process of organizing data in a database. This includes creating tables and establishing relationships between those tables according to rules designed both to protect the data and to make the database more flexible by eliminating redundancy and inconsistent dependency.

Redundant data wastes disk space and creates maintenance problems. If data that exists in more than one place must be changed, the data must be changed in exactly the same way in all locations. A customer address change is much easier to implement if that data is stored only in the Customers table and nowhere else in the database.

What is an "inconsistent dependency"? While it is intuitive for a user to look in the Customers table for the address of a particular customer, it may not make sense to look there for the salary of the employee who calls on that customer. The employee's salary is related to, or dependent on, the employee and thus should be moved to the Employees table. Inconsistent dependencies can make data difficult to access because the path to find the data may be missing or broken.

following links can be useful:

http://support.microsoft.com/kb/283878

http://neerajtripathi.wordpress.com/2010/01/12/normalization-of-data-base/

Answer 3

Edgar F. Codd, the inventor of the relational model, introduced the concept of normalization. In his own words:

1. To free the collection of relations from undesirable insertion, update and deletion dependencies;
2. To reduce the need for restructuring the collection of relations as new types of data are introduced, and thus increase the life span of application programs;
3. To make the relational model more informative to users;

4. To make the collection of relations neutral to the query statistics, where these statistics are liable to change as time goes by.

   — E.F. Codd, "Further Normalization of the Data Base Relational Model"

Taken word-for-word from Wikipedia:Database normalization

Answer 4

Check these out too:

• An Introduction to Database Normalization
• A Simple Guide to Five Normal Forms in Relational Database Theory