Retrieves the designated dataset, creates NCSS object, and
        creates a NCSS query object.

def set_dataset(self):
        '''
        Retrieves the designated dataset, creates NCSS object, and
        creates a NCSS query object.
        '''

        keys = list(self.model.datasets.keys())
        labels = [item.split()[0].lower() for item in keys]
        if self.set_type == 'best':
            self.dataset = self.model.datasets[keys[labels.index('best')]]
        elif self.set_type == 'latest':
            self.dataset = self.model.datasets[keys[labels.index('latest')]]
        elif self.set_type == 'full':
            self.dataset = self.model.datasets[keys[labels.index('full')]]

        self.access_url = self.dataset.access_urls[self.access_url_key]
        self.ncss = NCSS(self.access_url)
        self.query = self.ncss.query()