def _serialize
      attributes = {}
      _all_attributes.each do |attr|
        ivar = ('@' + attr.to_s).to_sym
        value = instance_variable_get(ivar)
        attributes[attr.to_s] = value.respond_to?(:is_poxreference?) ?
          POReference.new(value.id) : value
      end
      attributes
    end
def _serialize
      attributes = {}
      _all_attributes.each do |attr|
        ivar = ('@' + attr.to_s).to_sym
        value = instance_variable_get(ivar)
        attributes[attr.to_s] = value.respond_to?(:is_poxreference?) ?
          POReference.new(value.id) : value
      end
      attributes
    end
Return a single data structure that holds all persistent data for this
 class.