|First Normal Form||An entity is in First Normal Form (1NF) when all tables are two-dimensional with no repeating groups.
A row is in first normal form (1NF) if all underlying domains contain atomic values only. 1NF eliminates repeating groups by putting each into a separate table and connecting them with a one-to-many relationship. Make a separate table for each set of related attributes and uniquely identify each record with a primary key.
|Second Normal Form||An entity is in Second Normal Form (2NF) when it meets the requirement of being in First Normal Form (1NF) and additionally:
|Third Normal Form||An entity is in Third Normal Form (3NF) when it meets the requirement of being in Second Normal Form (2NF) and additionally:
|Boyce-Codd Normal Form||Boyce Codd Normal Form (BCNF) is a further refinement of 3NF. In his later writings Codd refers to BCNF as 3NF. A row is in Boyce Codd normal form if, and only if, every determinant is a candidate key. Most entities in 3NF are already in BCNF.
BCNF covers very specific situations where 3NF misses inter-dependencies between non-key (but candidate key) attributes. Typically, any relation that is in 3NF is also in BCNF. However, a 3NF relation won’t be in BCNF if (a) there are multiple candidate keys, (b) the keys are composed of multiple attributes, and (c) there are common attributes between the keys.
|Fourth Normal Form||An entity is in Fourth Normal Form (4NF) when it meets the requirement of being in Third Normal Form (3NF) and additionally:
|Fifth Normal Form||An entity is in Fifth Normal Form (5NF) if, and only if, it is in 4NF and every join dependency for the entity is a consequence of its candidate keys.|