This interface describes a control class that makes it
easy to find out if a particular User has a given Permission.
It also determines if a User has a a particular Role.
author: John D.
This class represents a set of Security Entities.
It makes it easy to build a UI.
It wraps a TreeSet object to enforce that only relevant
methods are available.
TreeSet's contain only unique Objects (no duplicates).
author: John D.