Abbreviation 2NF Year introduced 1971 | Developed by Edgar F. Codd | |
Second normal form database management system
Second normal form (2NF) is a normal form used in database normalization. 2NF was originally defined by E.F. Codd in 1971.
Contents
- Second normal form database management system
- Second normal form 2 nf dbms part 10
- 2NF and candidate keys
- References
A table that is in first normal form (1NF) must meet additional criteria if it is to qualify for second normal form. Specifically: a table is in 2NF if it is in 1NF and no non-prime attribute is dependent on any proper subset of any candidate key of the table. A non-prime attribute of a table is an attribute that is not a part of any candidate key of the table.
Put simply, a table is in 2NF if it is in 1NF and every non-prime attribute of the table is dependent on the whole of every candidate key.
Second normal form 2 nf dbms part 10
2NF and candidate keys
A functional dependency on part of any candidate key is a violation of 2NF. In addition to the primary key, the table may contain other candidate keys; it is necessary to establish that no non-prime attributes have part-key dependencies on any of these candidate keys.
Multiple candidate keys occur in the following table:
Even if the designer has specified the primary key as {Model Full Name}, the table is not in 2NF. {Manufacturer, Model} is also a candidate key, and Manufacturer Country is dependent on a proper subset of it: Manufacturer. To make the design conform to 2NF, it is necessary to have two tables: