rambabu sanaka

• Jan 18th, 2007

 

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.

• Eliminate duplicative columns from the same table.
• Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).

An entity is in Second Normal Form (2NF) when tables do not have composite primary keys. In other words, a table is in first normal form and all the non-key columns are functionally dependent on the entire primary key. Functional dependency means all other columns are dependent on the primary column.

A row is in second normal form if, and only if, it is in first normal form and every non-key attribute is fully dependent on the key. 

2NF eliminates functional dependencies on a partial key by putting the fields in a separate table from those that are dependent on the whole key. An example is resolving many:many relationships using an intersecting entity.

An entity is in Third Normal Form (3NF) when functional dependencies on non-key fields are eliminated by putting them in a separate table. At this level, all non-key fields are dependent on the primary key.

A row is in third normal form if and only if it is in second normal form and if attributes that do not contribute to a description of the primary key are move into a separate table