One of the most useful features of Adobe Flex Data Services 2 (FDS) is the capability to have a server update the connected clients in real time. This can be useful in many situations, such as updating inventory so clients can know what is in stock while they are still shopping, facilitating collaboration between disparate clients or even keeping sales dashboards updated to show completed sales as they happen. These features, and countless more, can now be easily integrated into your applications through the use of the Flex Message Services (FMS) of FDS.
Push technology is the capability for a server to send a message to the client without the client specifically requesting it. This makes it possible to have the client application automatically notified of updates as they happen. Over the years, this has been very difficult to implement for web-based applications. Developers have tried various solutions to "push" data from a server to a web client. They usually take the form of a "scheduled pull," so that on a set interval (maybe every 30 seconds or so) the client makes an HTTP request to the server asking for updated data. If anything new is available, the server returns it in its response. A classic example can be seen with gmail.com. When you have a web browser open to a logged-in gmail account, every 30 seconds the browser makes an HTTP request to the server, asking for new messages. Although this emulates "push" technology, it really is a scheduled pull, with the server responding only to a request. With Flash Media Server or XML sockets it has been possible to build push applications for Flash Player, although they have often not been trivial to implement.
One of the great features of FDS is the capability to easily register an application to listen for a type of notification from the server. Whenever the server broadcasts a message of that type, the Flex client responds and can be updated instantly with the new data. Imagine the possibilities of having a web portal instantly notify users of severe weather alerts, incoming e-mail, real-time scores of their favorite sports teams, or up-to-the-second stock quotes.