title: Communication mediator (controller?) between client and server
body: <p>I'm looking for implementing some sort of mediator (dispatcher/controller) between client app and server. 
  Client sends a command to mediator -> mediator processes (executes) the command. I use WCF as a platform for communication. Is there a way (pattern or smth) how I can add new commands to the client w/o changing the interface of the mediator?<br>
  Say mediator addresses  several other services which are hidden from the client. Client sends command to server to perform some action. These action involves various domain services and server side classes.
  Say later I decided to add a new command to the client. That new operation can be performed by domain services, but how can I trigger that action on remote machine, on domain services w/o having to extend mediator's interface (because mediator is the only communication point between clients and server).</p>
  
  <p>So generally, I'm looking for some kind of alternative to Controller in MVC pattern used in WEB apps, for not WEB app.</p>
  
  <p>Any ideas? Solutions?</p>