public function updateTimestamp($id, $data = null)
    {
        $self = $this;
        return $this->read($id)->then(
            function($dataStored) use ($self, $id, $data) {
                if (isset($data)) {
                    $dataStored = $data;
                }
                return $self->write($id, $dataStored);
            }
        )->then(
            function() { return true; }
        );
    }