Partial Dependency(Databases)

Question

I need closure on this. I fabricated a definition that partial dependency is when fields are indirectly dependent on the primary key or partially dependent but are also dep

Answer 1

Partial Dependency is one kind of functional dependency that occur when primary key must be candidate key and non prime attribute are depends on the subset/part of candidates key (more than one primary key).

Try to understand partial dependency relate through example :

Seller(Id, Product, Price)

Candidate Key : Id, Product
Non prime attribute : Price

Price attribute only depends on only Product attribute which is a subset of candidate key, Not the whole candidate key(Id, Product) key . It is called partial dependency.

So we can say that Product->Price is partial dependency.

Answer 2

Partial dependence is solved for arriving to a relation in 2NF but 2NF is a "stepping stone" (C. Date) for solving any transitive dependency and arriving to a relation in 3NF (which is the operational target). However, the most interested thing on partial dependence is that it is a particular case of the own transitive dependency. This was demostrated by P. A. Berstein in 1976: IF {(x•y)→z but y→z} THEN {(x•y)→y & y→z}. The 3NF synthesizer algorithm of Berstein does not need doing distintions among these two type of relational defects.

Answer 3

Partial dependency means that a nonprime attribute is functionally dependent on part of a candidate key. (A nonprime attribute is an attribute that's not part of any candidate key.)

For example, let's start with R{ABCD}, and the functional dependencies AB->CD and A->C.

The only candidate key for R is AB. C and D are a nonprime attributes. C is functionally dependent on A. A is part of a candidate key. That's a partial dependency.