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Codd's Normal Forms

Dr.Edgar (Ted) Codd was employed by IBM at their Almaden Research Laboratories
in the San Jose area, when he published his definitive paper in 1970, entitled :-
"A Relational Model of Data for Large Shared Data Banks".

The beauty of the Normalized approach is that it provides a clear theoretical foundation 
   for the design of a database.
This is a distinct advantage over the design of object-Oriented Data Models. There is
   no agreed standard for modelling the real world with its behaviour and therefore 
O-O modelling is subjective and often reduces to squabbling and argument.   
However, thanks to Ted Codd, there is a prescribed 
   approach which can be guaranteed to produce well-designed databases.

The process of producing a Normalized design results in the definition of a number of Tables
and relationships between the Tables.
Normalization can be summarised as one where the Word of Codd, is :-
"The data in a record depends on the Key to the record, the Whole Key, and 
 nothing but the Key, so help me Codd."
For example, total figures would not appear in a normalized database because they
can be derived from the individual figures. 

(1) In relational database design, the process of organizing data to minimize duplication. 
    Normalization usually involves dividing a database into two or more tables and defining
    relationships between the tables. 
    The objective is to isolate data so that additions, deletions, and modifications of a 
    field can be made in just one table and then propagated through the rest of the database
    using the defined relationships. 

2) There are three main normal forms, each with increasing levels of normalization: 
   2.1 First Normal Form (1NF): Each field in a table contains different information. 
       For example, in an employee list, each table would contain only one birthdate field. 
   2.2 Second Normal Form (2NF): No field values can be derived from another field. 
       For example, if a table already included a birthdate field, it could not also include a 
       birth year field, since this information would be redundant. 
   2.3 Third Normal Form (3FN): No duplicate information is permitted. 
       So, for example, if two tables both require a birthdate field, the birthdate information 
       would be separated into a separate table, and the two other tables would then access the 
       birthdate information via an index field in the birthdate table. Any change to a birthdate 
       would automatically be reflect in all tables that link to the birthdate table. 

   There are additional normalization levels, such as Boyce Codd Normal Form (BCNF), 
   Fourth Normal Form (4NF) and Fifth Normal Form (5NF). 
   While normalization makes databases more efficient to maintain, they can also 
   make them more complex because data is separated into so many different tables. 

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