Second Normal Form (2NF)
Second Normal Form (2NF) is introduced by E.F. Codd based on Functional Dependency. Each 1NF entity must be implies with 2NF that helps to identify and eliminate redundant information from 1NF entity to avoid update and delete anomalies.
2NF definition is "a 1NF entity is in 2NF if and only if none of its non-prime attributes are functionally dependent on a part of a candidate key (Primary Key). 2NF is used to produce composite candidate keys in 1NF Entity through decomposition of the 1NF entity into two different entities that avoid partial functional dependency."
An instance, the 1NF Employee_Skills entity is maintains redundant data in the Skill_Name attribute that non-prime attribute is functionally dependent on a part of candidate key Emp_Code primary key attribute. According to the 2NF, the Employee_Skills entity can decompose into Employee_Skills and Skill_Master entities to avoid redundant data.
2NF is produce composite candidate keys in the 1NF Employee_Skills entity, when alter the Skill_Name non-prime attribute into Skill_Code primary key attribute based on referential integrity constraints between Employee_Skills and Skill_Master entities. This composite candidate key is provides full functional dependency between Emp_Code and Skill_Code attributes.
The decomposed Employee_Skills entity can relate with Skill_Master entity through common Skill_Code attribute and Referential Integrity Constraints.
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