@abstractmethod<EOL><INDENT>def next(self):<DEDENT>
raise StopIteration<EOL>
r"""
        Called by the framework to provide a key/value pair to the
        :class:`Mapper`\ . Applications must override this, making
        sure it raises :exc:`~exceptions.StopIteration` when there are no more
        records to process.

        :rtype: tuple
        :return: a tuple of two elements. They are, respectively, the
          key and the value (as strings)