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Explain about partial and fully functional dependency
If a non-key attribute(s) depends on a part of a candidate key then it is partial dependency, it is applicable where the primary key has multiple attributes. If a non-key attribute(s) depends on the entire candidate key, then it is full dependency.
Example 1
Let R(A,B,C) and AB=candidate key.
A-> C is a partial dependency (where C dependson a part of the candidate key).
AB->C is a full dependency (where c depends on the entire candidate key).
A Functional dependency X->Y is a partial dependency if,
- X is a part of candidate key and
- Y is a non-key attribute(s).
Example 2
R(ABCDE)
F: {AB->C, C->D, B->E }. Find partial dependency.
Solution
AB+ =ABCD C+= CD B+= BE
=>AB is the only candidate key.
=> key attributes =A,B and
=> non-key attributes = C,D,E.
Key attributes are also called prime attributes and non-key attributes are also called non-prime attributes.
AB->C is not a Partial dependency // it is full dependency.
C-> D is not a partial dependency //it is full dependency.
B-> E is a partial dependency, since B is a part of the candidate key and E is a non-key attribute.
Example 3
Consider another example which is given below −
StudentClass (CourseID, RollNoOfStudent, Score, StudentName, StudentAge);
The Candidate Key in the above relation is {CourseID, RollNoOfStudent}
The functional dependency is; {CourseID, RollNoOfStudent} —-> {Score}
Now, the score is fully dependent on course id and rollno of student ..
{RollNoOfStudent}--->{StudentName}
Now student name is a non primary attribute, and it depends only on a subset of candidate keys, not on whole.
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