Functional Dependence (Fd)

Student_Activity
SID       Activity         Fee
100       Skiing           200
150       Swimming          50
175       Squash            50
200       Swimming          50

Overview

The secret of normal forms is to realize that some attribute values determine other attribute values. In the case above, the activity fee was dependent on the activity, not the student. If a determinant (activity in the above case) cannot be a key in the relation, those attributes that depend on the determinant will repeat each time the value for the determinant repeats (see swimming in the original relation above). To prevent determinant values from repeating it is best to create a separate relation where the determinant is a key (remember keys can't repeat). This is what we did when we split the original relation into two relations.

--oldweb normalization article

Student
SID       Activity
100       Skiing
150       Swimming
175       Squash
200       Swimming

ActivityFees
Activity  Fee
Skiing    200
Swimming  50
Squash    50