@abc.abstractmethod<EOL><INDENT>def assign_comment_to_book(self, comment_id, book_id):<DEDENT>
pass<EOL>
Adds an existing ``Comment`` to a ``Book``.

        :param comment_id: the ``Id`` of the ``Comment``
        :type comment_id: ``osid.id.Id``
        :param book_id: the ``Id`` of the ``Book``
        :type book_id: ``osid.id.Id``
        :raise: ``AlreadyExists`` -- ``comment_id`` is already assigned to ``book_id``
        :raise: ``NotFound`` -- ``comment_id`` or ``book_id`` not found
        :raise: ``NullArgument`` -- ``comment_id`` or ``book_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*