Interesting problem, have you considered leveraging JMS as the backend to perform the publish subcribe portion with a service front end that allows a new request to be posted?
My 2 cents, sounds like an interesting services challenge.
Have you checked out WS-Eventing in JBossWS? I've not personally looked at it beyond the content of the user guide however it sounds very much like what you are looking for.
Please let us know as I'm curious to hear the various real world use cases for this standard.
What kind of business problem are you trying to solve with Pub-Sub in web services? Are any non-Java technologies being used and need to participate?
Now I had a look at WS-Eventing, it seems to be the solution to the problem I have.
My use case for it is -as I think- quite common. It is from workflow management, where business processess (e.g. implemented as web services) can issue user tasks to a web service called task manager (that would be the publisher). When a user has completed, the process (the subscriber) is asynchronously informed about that.
In the future, we will implement our processes in BPEL, and also .NET web services should be able to issue tasks. So the publisher is Java (at the moment, it is running on JBossWS4EE), and the subscribers can be anything that is able to interact as a web service client.
Thanks for your information,