kiran_oleti

• Dec 17th, 2005

 

4types

samiksc

 Profile Answers by samiksc 

• Jan 18th, 2006

 

There are 5 normal forms. It is necessary for any database to be in the third normal form to maintain referential integrity and non-redundance.

1. First Normal Form: Every field of a table (row,col) must contain an atomic value
2. Second Normal Form: All columns of a table must depend entirely on the primary key column.
3. Third Normal Form: All columns of a table must depend on all columns of a composite primary key.
4. Fourth Normal Form: A table must not contain two or more independent multi-valued facts. This normal form is often avoided for maintenance reasons.
5. Fifth Normal Form: is about symmetric dependencies.

Each normal form assumes that the table is already in the earlier normal form.

jackson

• Jan 31st, 2006

 

definition : normalization is organizing data in database.

aruna

• Apr 3rd, 2006

 

Normalisation is nothing but organising database data into number of tables.

4 types of normal forms.

Ranjeev

• Apr 26th, 2006

 

Normalisation can be defined as a process to minimize, infact eliminate redundancy of data within the database. It first requires that redundancy is detected through the proper use of FD's( Functional Dependency). Some explanation:-- let R be a relation and S be a set of all attributes of R.-- let A & B be two sets which are subsets of S.( A & B can be singleton Sets)-- Now, A --> B ( A Functionaly Defines B ) if and only if each tuple of A has a corresponding value in B , in other words if two tuples of A agree on a value, they must agree on their B value. ( Else there is no FD between A & B.-- if A is not the candidate or super Key, and the FD is non-trival i.e. B is not the subset of A then there is redundancy of data.Note :Normalisation is the procedure to minimize redundancy.-- let S1 be a set of all the FD's within the Relation R.-- develop a closure of Set S1+ with minimum no. of FD's which in turn satisfies all the FD's of Set S1 -- there are several rules that help in normalising a Relation.-- we have come upto 5th Normalised forms but it is not end.

rangunagaraj

 Profile Answers by rangunagaraj 

• Jul 5th, 2007

 

NORMALIZATION is a body of rules addressing analysis and conversion of data structures into relations that exhibit more desirable properties of internal consistency,minimal redundancy and maximum stability.

FIRST NORMAL FORM: A relation is in the first normal form if it does not contain any repeating elements or groups.

SECOND NORMAL FORM: A relation is said to be in the seond normal form if it is in first normal form and all non-key attrinutes are are fully functionally dependent on on primary key.

THIRD NORMAL FORM: A relation is said to be in third normal form if it is in second normal form and every  attribute is independent of all other non-key attributes.