Hi! could you kindly tell me where can I study about FD simply and clearly. Kindly give me links of the sites. I'm completely lost and can't understand about FD. May be my mathematical skill isn't very good
Try Functions versus Relations, and let me know if you have any questions. A functional dependency is just asking whether one value is a function of another. If you know fact A, can you determine fact B? If so, B has a functional dependency on A.
For example, given a person's social security or national identity number, could you determine the person's birthday? In society, it may be difficult but since it's generally understood that those numbers uniquely identify a physical person, and that a person has a particular birthday, we can say that birthday has a functional dependency on social security number.
Turning the relationship around, a given date doesn't determine a specific social security number, lots of people with different numbers are born on the same date. Social security number doesn't have a functional dependency on birthday.