Editing Functional dependency (section)

=== Lectures ===
This example illustrates the concept of functional dependency. The situation modelled is that of college students visiting one or more lectures in each of which they are assigned a teaching assistant (TA). Let's further assume that every student is in some semester and is identified by a unique integer ID.

{| class="wikitable"
|-
! Student ID !! Semester !! Lecture !! TA
|-
| 1234 || 6 || Numerical Methods || John
|-
| 1221 || 4 || Numerical Methods || Smith
|-
| 1234 || 6 || Visual Computing || Bob
|-
| 1201 || 2 || Numerical Methods || Peter
|-
| 1201 || 2 || Physics II || Simon
|}

We notice that whenever two rows in this table feature the same StudentID,
they also necessarily have the same Semester values. This basic fact
can be expressed by a functional dependency:
* StudentID → Semester.

If a row was added where the student had a different value of semester, then the functional dependency FD would no longer exist. This means that the FD is implied by the data as it is possible to have values that would invalidate the FD. 

Other nontrivial functional dependencies can be identified, for example:
* {StudentID, Lecture} → TA
* {StudentID, Lecture} → {TA, Semester}

The latter expresses the fact that the set {StudentID, Lecture} is a [[superkey]] of the relation.