|Codd's Normal Forms|
THE MAN :
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 :-
HIS NORMAL FORMS :
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.