A relation is a function if the value in its Domain does not occur more than once. This means each domain value is paired with exactly one value of range.
In the given scenario, the domain is the students (e.g name of a student) and the function returns the date of birth of the student. A student can have only one date of birth. So it is not possible that a value in Domain(i.e. a student) is paired with more than one date of births.
Therefore, we can conclude that the given relation describes a function.
