protected function create()
    {
        // if user_id and license_key are set then use the web service
        if (array_get($this->config, 'user_id', false)) {
            return $this->createWebClient();
        }

        // if database file is set then use database service
        if (array_get($this->config, 'database', false)) {
            return $this->createDatabase();
        }

        throw new InvalidCredentialsException();
    }