## Normal Forms – Basic Rules and Solutions

### First Normal Form (1NF)

A relation schema R is in 1NF if and only if,

- All the attributes of the relation are atomic (indivisible into meaningful sub parts),
- Every attribute contains single value (per record).

#### How to convert un-normalized table into 1NF normalized table?

Expand the table by duplicating records for every value of multi-valued
attributes (Flatten the table).

### Second Normal Form (2NF)

A relation schema R is in 2NF if and only if,

- At the first place the table is in 1NF,
- All the non-key attributes of the table are fully functionally dependent on the Primary key of the table.

#### How to convert un-normalized or 1NF table into 2NF normalized table?

It can be done using decomposition. That is, by breaking Non-2NF
relations into smaller tables using the Functional Dependencies derived.

### Third Normal Form (3NF)

A relation schema R is in 3NF if and only if,

- The table is in 2NF,
- There is no Functional Dependency such that both Left Hand Side and Right Hand Side attributes of the FD are non-key attributes. In other words, no transitive dependency is allowed.

#### How to convert un-normalized or 2NF table into 3NF normalized table?

It can be done using decomposition. That is, by breaking Non-3NF
relations into smaller tables using the Functional Dependencies derived. Especially,
by creating a separate table for non-key attributes dependencies.

###

A relation schema R is in BCNF if an only if,

###
__Boyce-Codd Normal Form (BCNF)__

A relation schema R is in BCNF if an only if,

- The table is in 3NF
- For all the non-trivial FDs held on R, the left hand side of those non-trivial FDs must be Candidate Keys.

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