public PubSubService.UniqueIdentifier getServiceIdentifier()
        {
            return new PubSubService.UniqueIdentifier( serviceId );
        }
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