@abc.abstractmethod<EOL><INDENT>def get_result_size(self):<DEDENT>
return<EOL>
Returns the size of a result set from a search query.

        This number serves as an estimate to provide feedback for
        refining search queries and may not be the number of elements
        available through an ``OsidList``.

        :return: the result size
        :rtype: ``cardinal``


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