public function read($sessionId) {
        try {
            // try to retrieve the session content first to see if it exists
            $result = $this->_tableRestProxy->getEntity($this->_sessionContainer, $this->_sessionContainerPartition, $sessionId);
            // get the entity instance
            $entity = $result->getEntity();
            // deflat the serialized data
            return unserialize(base64_decode($entity->getPropertyValue('data')));
        } catch (ServiceException $e) {
            // the entity doesn't exist, return empty string according to the spec:
            //   http://www.php.net/manual/en/sessionhandlerinterface.read.php
            return '';
        }
    }