module ActiveFedora::WithMetadata::ClassMethods

def MetadataNode(parent_klass)

parent_class attribute to have the value of the current class.
Make a subclass of MetadataNode named GeneratedMetadataSchema and set its 
def MetadataNode(parent_klass)
  klass = const_set(:GeneratedMetadataSchema, Class.new(MetadataNode))
  klass.parent_class = parent_klass
  klass
end

def metadata(&block) 

def metadata(&block)
  metadata_schema.exec_block(&block)
end

def metadata_schema 

def metadata_schema
  @metadata_schema ||= MetadataNode(self)
end