This is more a theoretical question than a practical one, but given I undestand the principles of SOA I am still a bit unsure about if this can be applied to any app.
The usual example is where a client wants to know something from a server thus we implement a service that can provide that information given a client request, it can be stateless or statefull, etc.
But what happens when we want to be notified when something happens on the server, maybe we call a service to register a search and want to be notified when a new item arrives to the server that matches or search.
Of course that can be implemented using polling and leverage that using long timeouts, but I can not see a way in the usual protocols to receive events from the server without making a call to ask.
If you can point me to an example, or tell me an architecture that could support then you have made my day.
Have you considered pub-sub (ie; WS-Eventing, WS-Notification)? These are the usual means to pushing “stuff” to interested consumers/subscribers.