def start(cls, ev=None):
        """
        Start the query to aleph by ISSN.
        """
        ViewController.log_view.add("Beginning AlephReader request..")

        ViewController.issnbox_error.reset()
        issn = ViewController.issn.strip()

        # make sure, that `issn` was filled
        if not issn:
            ViewController.issnbox_error.show("ISSN nebylo vyplněno!")
            ViewController.log_view.add("No ISSN! Aborting.")
            return

        ViewController.issnbox_error.hide()
        ViewController.issn_progressbar.reset()
        ViewController.issn_progressbar.show(50)
        ViewController.log_view.add("For ISSN `%s`." % issn)

        make_request(
            url=join(settings.API_PATH, "aleph/records_by_issn"),
            data={'issn': issn},
            on_complete=cls.on_complete
        )