Hi,
My application must have features for getting formula from users, validate it and calculate it.
These formulas use in HRM syetem.
So you mentioned above is functional requirement so there is a class which is which deals with the user to recieve formula and there is another class which validate the formula and there is another class which calcualte the formula.
You should build your structure diagram ( class diagram) based on your functional definiton and establish the association between these classes. Then think about what
patterns do you have in your OO design. I can see visitor pattern for validation of the formula. And a factory pattern for producing different class implementation for different formula or ??
Regards,
Alan Mehio
London,UK