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# Differentiate between Partial Dependency and Fully Functional Dependency

• Last Updated : 25 Jun, 2021

Fully Functional Dependency :
If X and Y are an attribute set of a relation , Y is fully functional dependent on X, if Y is functionally dependent on X but not on any proper subset of X.
Example  –
In the relation ABC->D , attribute D is fully functional dependent on ABC if it is fully functional dependent on ABC and not on any proper subset of ABC. That means that subsets of ABC like AB ,BC ,A,B ,etc cannot determine D .
Let us take another example –

Supply table

From the table, we can clearly see that neither supplier_id  nor item_id can uniquely determine price but both supplier_id and item_id together can do so. So we can say that price is fully functionally dependent on { supplier_id , item_id } .This summarizes and gives our fully functional dependency −

`{ supplier_id , item_id } -> price`

Partial Functional Dependency :
A functional dependency X->Y is a partial dependency if Y is functionally dependent on X and Y cannot be determined by any proper subset of X.
For example , we have a relationship  AC->B , A->D and D->B.
Now if we compute closure of {A+}=ADB
Here A is alone capable of determining B, which means B is partial dependent on AC .
Let us take another example –

Student table

Here , we can see that both the attributes name and roll_no alone is able to uniquely identify a course. Hence , we can say that the relationship is partial dependent .

Differences between Full Functional Dependency and Partial Functional Dependency are :

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