ded in the macro
<code>
BOOST_SERIALIZATION_BASE_OBJECT_NVP
</code>
is code which links derived and base class definitions in tables used to serialize
derived classes through pointers to a polymorphinc base class.  This code requires
the ability to invoke
<code>
static_cast&lt;Base &&gt;(Derived &)
</code>
which C++ will only permit from within the derived class if the base class is 
private or protected. The program will fail to compile with an error message 
indicating invalid cast.
<p>
In order for this
