public function get_unique_id() {
        global $CFG;

        if (!is_null($this->uniqueid)) {
            return $this->uniqueid;
        }

        // Generate a unique id for this site, this model and this time splitting method, considering the last time
        // that the model target and indicators were updated.
        $ids = array($CFG->wwwroot, $CFG->prefix, $this->model->id, $this->model->version);
        $this->uniqueid = sha1(implode('$$', $ids));

        return $this->uniqueid;
    }