DBMS Full functional dependency(FFD)

Full functional dependency(FFD)

The term full functional dependency (FFD) is used to indicate the minimum set of attributes in of a functional dependency (FD). In other words, the set of attributes X will be fufunctionally dependent on the set of attributes Y if the following conditions are satisfied: 

  • X is functionally dependent on Y and
  • X is not functionally dependent on any subset of Y.
 In relation ASSIGN of table  it is true that
FD: {EMP-ID,PROJECT, PROJECT-BUDGET}  -> {YRS-SPENT-BY-EMP-ON PROJECT}

 The values of EMP-ID, PROJECT and PROJECT-BUDGET determine a unique value of YRS-SPENT-BY-EMP-ON-PROJECT. However, it is not a full functional dependency because neither the EMP-ID -> YRS-SPENT-BY-EMP-ON-PROJECT nor the PROJECT -> YRS-SPENT-BY-EMP-ON-PROJECT holds true.
In fact, it is sufficient to know only the value of a subset of {EMP-ID, PROJECT, PROJECTBUDGET), namely, {EMP-ID, PROJECT}, to determine the YRS-SPENT-BY-EMP-ON PROJECT.  Thus, the correct full functional dependency (FFD) can be written as:
 FD: {EMP-ID,PROJECT} -> {YRS-SPENT-BY-EMP-ON-PROJECT}

 
Relation R1:BUDGET
PROJECT PROJECT-BUDGET
P1 INR 100 CR
P2 INR 150 CR
P3 INR 200 CR
P4 INR 100 CR
P5 INR 150 CR
P6 INR 300 CR


 
Relation R2:ASSIGN
EMP-NO PROJECT YRS-SPENT-BY-
EMP-ON-PROJECT
106519 P1 5
112233 P3 2
106519 P2 5
123243 P4 10
106519 P3 3
111222 P1 4



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