@abc.abstractmethod<EOL><INDENT>def has_child_books(self, book_id):<DEDENT>
return<EOL>
Tests if a book has any children.

        :param book_id: a book ``Id``
        :type book_id: ``osid.id.Id``
        :return: ``true`` if the ``book_id`` has children, ``false`` otherwise
        :rtype: ``boolean``
        :raise: ``NotFound`` -- ``book_id`` is not found
        :raise: ``NullArgument`` -- ``book_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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