Is it ever valid to convert an object from a base class to a subclass

Question

In my application at the moment I have (as in so many other applications) an entity called Contact, which represents any person. At its most basic level this is

Answer 1

Contact is an attribute of Employee. Worker (your Employee) is a role, Manager is a role. Worker and Manager are both still Employee, but have Roles. Role is an IS IN relationship, Employee is an AM A relationship, and Contact is a HAS A relationship. Employee HAS A Contact (1-1 relationship) One contact per employee (1-M if they have two phones etc but I digress) Employee IS IN Role (M-M relationship) Many employees many Roles Employee Is A (M-1 relatiohship) - Many employees, all of employee type.

So you are changing roles.