Functional Dependency in RDBMS

Functional Dependency in RDBMS

Functional Dependency

  • Functional Dependency
  • Full Functional Dependency
  • Partial Dependency
  • Transitive Dependency

Functional Dependency:
Given a Relation R(A,B,C,D), Where A,B,C,D are attributes.

Functional Dependencies A→BCD , BC→D .

A→BCD means A functionally determines BCD.
BC→D means BC functionally determines D.

Full Functional Dependency:
Given a relation R and Functional Dependency X→Y
Y is fully functionally dependent on X and there should not be any Z→Y, Where Z is a proper subset of X.


Partial Dependency:
If any proper subsets of the key determine any of the non-key attributes then there exist a partial dependency.

Example: Given a relation R(A,B,C,D,E) , Functional Dependency : AB→CDE , Primary_key(or simply 'key') is AB.

Then    A→C : is a Partial Dependency
            A→D :  is a Partial Dependency
            A→E : is a Partial Dependency
            B→C : is a Partial Dependency
            B→D : is a Partial Dependency
            B→E : is a Partial Dependency

 


Transitive Dependency

 Given a relation R(A,B,C,D,E)  then dependency like A-->B, B-->C   is a transitive dependency, since   A-->C is implied .