relational-databaserdbmsdatabase-normalizationfunctional-dependenciescandidate-key

what is Partial Dependency


Suppose we have a relation R(A,B,C,D,E) with candidate keys {A,B} , {C,D} and let E be a non prime attribute.

If there is a dependency C->E then it is partial dependency as E depends on a part of candidate key {C,D}

Is dependency BC->E partial?


Solution

  • A functional dependency is partial if, on removing one or more attributes from the determinant (left-hand side), you still have a dependency that holds. In your example therefore:

    {C}→{E} is a full functional dependency

    {C,D}→{E} is a partial functional dependency because {C}→{E}

    {B,C}→{E} is a partial functional dependency because {C}→{E}