protected function should_cascade_delete($rel)
	{
		// Because temporal includes soft delete functionality it can be deleted too
		if ( ! is_subclass_of($rel->model_to, 'Orm\Model_Soft') && ! is_subclass_of($rel->model_to, 'Orm\Model_Temporal'))
		{
			// Throw if other is not soft
			throw new RelationNotSoft('Both sides of the relation must be subclasses of Model_Soft or Model_Temporal if cascade delete is true. '.$rel->model_to.' was found instead.');
		}

		return true;
	}