@Override
        public String toString()
        {
            return "UniqueIdentifier{" +
                "serviceId='" + serviceId + '\'' +
                ", nodeId='" + nodeId + '\'' +
                ", itemId='" + itemId + '\'' +
                '}';
        }
A unique identifier for an item, in context of all nodes of all services in the system.

The properties that uniquely identify an item are its node, and its itemId.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/PublishedItem.java