def get_book_query(self):
raise errors.Unimplemented()<EOL>
Gets the query for a book query.

        Multiple retrievals produce a nested ``OR`` term.

        return: (osid.commenting.BookQuery) - the book query
        raise:  Unimplemented - ``supports_book_query()`` is ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_book_query()`` is ``true``.*