Understanding and mastering database normalization techniques is essential in order to achieve a high performance database design for your system. If your design doesn't conform to (at least) the Third Normal Form (3NF), chances are high that you will find it hard to achieve the performance needed for a successful application.
Furthermore, you will find that writing good DML-statements (SELECT, UPDATE, INSERT or DELETE) is difficult, and sometimes actually impossible, without using a lot of procedural coding (PL/SQL in Oracle, VB/C# in Microsoft products).
Many "experts" will tell you that if you do database normalization up to (and including) the Third Normal Form, you're well off. The Database Normalization eBook shows you that this a far too easy approach, and it is richly documented with graphical Entity Relationship and Server Diagram examples. for more Detail Click Here!