Invalid accessibility (Reviewer Review)
Only inner classes may use private or protected accessibility (on the class itself).
Superclasses should be at least as accessible as their subclasses.
Operation return data types should be at least as the operations themselves.
Attribute data types should be at least as the attributes themselves.
Parameter data types should be at least as the operations themselves.
Consequences
The model will not be able to be implemented.
Strategy
Change the accessibility of the items.