The training material for a well-known database system includes an example employee class with standard attributes such as employee ID, name, and so on.

The same entity also includes both a salary attribute and a commission attribute, even though only sales representatives earn a commission. There are also some employees that are not on salary but they are paid an hourly wage. To summarize, there are employees paid on any hourly basis, employees that are paid salary only and sales employees that earn both salary and commission.

In their lesson plans, this vendor emphasizes various ways that their software can handle the inevitable null values of the commission attribute.

I believe that their one class for all employee attributes model is simply wrong.

Design a way to preserve the salary and commission and hourly wage information without allowing null values in any of the attributes.

Draw the class diagram and the relation scheme.