module ActiveFedora::Inheritance::ClassMethods

Abstract classes can't have default scopes.

def abstract_class?
  self == Base
end

and C.base_class would return B as the answer since A is an abstract_class.
If B < A and C < B and if A is an abstract_class then both B.base_class

through some arbitrarily deep hierarchy, B.base_class will return A.
If A extends ActiveFedora::Base, A.base_class will return A. If B descends from A

an abstract class, if any, in the inheritance hierarchy.
Returns the class descending directly from ActiveFedora::Base, or

def base_class
  return File if self <= File
  raise ActiveFedoraError, "#{name} doesn't belong in a hierarchy descending from ActiveFedora" unless self <= Base
  if self == Base || superclass == Base || superclass.abstract_class?
    self
  else
    superclass.base_class
  end
end