Five normal forms in Database Design

[Gonercase]

I want to be a database administrator and for which I am going to join a institution soon. Till then I have started learning about the database management systems on my own by searching things on an forums. Now I have came across some topic that if you wan to make a better database then you must follow normal forms Database Design, there are total 5. Does anybody here know that what are the Five normal forms in Database Design.

[Steyn]

In order to develop the required tables, there are simple DBs in principle two possibilities: either obstinate in Schedule-F for the five normal forms or something more intuitive ER model, possibly followed by control the five normal forms. Only when you develop larger databases, you must work simultaneously with both possibilities. That is, set only with the ER model, a basic structure and review it with the five normal forms.

[Ronchi]

The normal forms are a set of rules with which one can check whether a data model can implement clean using a relational DBMS. This is known as normalization.

The 1st Normal form : A relation type is in the 1 Normal form if all attributes have a value up. At the intersection of a column with a maximum range may therefore be a data value. The absence of data is allowed. In other words, repeating groups are not allowed.

[Author]

The 2nd Normal form : A relation type is in the 2nd Normal form if, in the 1 Normal form and attribute the entire primary key of each dependent. Relations types, the first in the Normal form, shall automatically be in the 2 Normal form if its primary key is not composite.

The 3rd Normal form : It is satisfied if the second Normal form is true and the non-key attributes functionally independent. If A and B attributes of a type of relations, then B is functionally dependent on A if for every occurrence of the same value of A must always occur the same value of B. A functional dependency may be established by a group of attributes.

[Villiers]

The 4th Normal form : The 4th Normal form is satisfied if the 3rd Normal form is true and if no pairs occur multivalued dependencies are present. If A, B and C attributes of a type relations, so C is multi-valued function of A, if for any value of A for all values of B, found in association with this value of A, must occur in each case the same set of values of C. For different values of A may occur different sets of values of C. In violation of the 4th Normal form, Groups inconsistencies occur.

The 5th Normal form :A relation type is in the 5th Normal form if, in the 4th Normal form and he can make under any circumstances, by combination of simpler types of relations with different keys. That's fairly self-explanatory, right?

[justinepeter]

First Normal Form
A relation R is in first normal form (1NF) if and only if all underlying domains contain atomic values only.

Second Normal Form
A relation R is in second normal form (2NF) if and only if it is in 1NF and every nonkey attribute is fully dependent on the primary key.

Third Normal Form
A relation R is in third normal form (3NF) if and only if it is in 2NF and every nonkey attribute is nontransitively dependent on the primary key.

Boyce/Codd Normal Form

A relation R is in Boyce/Codd normal form (BCNF) if and only if every determinant is a candidate key.

Fourth Normal Form

A relation R is in fourth normal form (4NF) if and only if, wherever there exists an MVD in R, say A -> -> B, then all attributes of R are also functionally dependent on A. In other words, the only dependencies (FDs or MVDs) in R are of the form K -> X (i.e. a functional dependency from a candidate key K to some other attribute X). Equivalently: R is in 4NF if it is in BCNF and all MVD’s in R are in fact FDs.

Fifth Normal Form
A relation R is in fifth normal form (5NF) – also called projection-join normal form (PJ/NF) if and only if every join dependency in R is a consequence of the candidate keys of R.

[Vandam]

Generally, one can use the tables that have been obtained for the five normalization, 1-1 in the DB. It must, however, if one has not been rage normalization the tables very torn apart. Tables that have the same primary key can be folded easily, without violating the normalization form of notices. For large data sets with high traffic, it may be advisable, however, in part, for performance reasons to restore some denormalization. Here, one can say that it is less of a problem with not changing data against the normal forms and notices. In fact this eliminates the problem that can be changed when changing, not all data and results in a contradiction. Nevertheless, one should always be clear about when they violated the normal forms!