05-07-2012, 11:51 AM
Normalization
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INTRODUCTION
Normalization is a technique to generate a set of relation that allow store information without unnecessary redundancy but in same time allow retrieve information easily.
Database normalization is the process of removing redundant data from tables in to improve storage efficiency, data integrity, and scalability.
In the relational model, methods exist for quantifying how efficient a database is. These classifications are called normal forms (or NF), and there are algorithms for converting a given database between them.
Normalization generally involves splitting existing tables into multiple ones, which must be re-joined or linked each time a query is issued.
2nd Normal Form
A relation is set to be a 2nd NF if it is in 1st NF.
Every non key attribute on functionaly dependent
on primary key.
3rd Normal Form
A relation is set to be in 3rd NF if it is 2nd NF .
Every non key attribute is functional dependent on any other non – key attributes
(then we required 3rd NF) .
In this table roll no is primary key and all other attribute are functional dependent on it .But the same time we know that every part – 1 student are accommodate in ganga hostel.
Part – 2 student kaveri , part – 3 student in Krishna and
part – 4 student Godavari.
BCNF (BOYCE- CODD NORMAL FORM)
BCNF requires that the table is 3NF and only determinants are the candidate keys.
A Relation has more than one possible keys have a common attribute if an attribute of a composite key dependent on an attrite of other composite key.