ISRO | ISRO CS 2018 | Question 75

The set of attributes X will be fully functionally dependent on the set of attributes Y if the following conditions are satisfied.
(A) X is functionally dependent on Y
(B) X is not functionally dependent on any subset of Y

(C) Both (a) and (b)
(D) None of these


Answer: (C)

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

i)  X is functionally dependent on Y and
ii) X is not functionally dependent on any
    subset of Y.

Example: In relation StuGrade:

{stud_id, course_id, course_name} -> {course_grade}

The values of stud_id, course_id, course_name determine a unique value of course_grade. However, it is not a full functional dependency because it is sufficient to know only the value of a subset of {stud_id, course_id, course_name}, namely, {stud_id, course_id}, to determine the course_grade Thus, the correct full functional dependency can be written as:

{stud_id, course_id} -> {course_grade}

So, option (C) is correct.


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