Client-Server architecture?

I have to create an application that based on repository of something, and when there is new update n the repository do something to the registred user. something like inverse client-server (as the server open contant t开发者_运维问答he users). I hope it's clear enough. the code is written in C# 4.0. What is the best architecture to do such thing?

What you are talking about is Duplex messaging.

Check this out http://msdn.microsoft.com/en-us/library/ms731064.aspx

This enables two way messaging between a client and a server.