Functional dependencies are not equations

Question

In which case the functional dependencies are not equations? Describe briefly?

Answer 1

Equations are deal with numerical relationships. A functional dependency is deals with the existence of a determinant relationship between characteristics, regardless of whether or not there is a numerical relationship between them. Therefore, if we know that there is no hot water every Sunday; No-Hot-Water is functionally dependent on Sunday. Hence if we know it is Sunday, then we know we will have No-Hot-Water. That is a functional dependency, but it is not an equation.