Re: The "Presentation" Layer

john e wrote:

A green-screen terminal is also a peer in the network, but in practice it acts more as a server, and the program running on the host is the client. E.g. the program requests the terminal to display a format. So most of the time a terminal takes on the server role. However, at first, when logging into the system, a terminal initiates a session and has the client role.

This is a great explanation, John, and is why I call the traditional 5250 type of application "server/client" to differentiate from "client/server". With server/client, the user actually communicates with the server device, such as the 5250 terminal. The component running on the host is actually the client, sending requests to the server. That's in fact why my product is called "PSC" which stands for "PBD Server Client".

The entire page-at-a-time browser interface all the way up to JSP Model 2 has been server/client, which is why the browser was such a good replacement for 5250. With the popularity of AJAX, however, we've changed to a client/server model, in which the user talks to the client, which is typically a JavaScript application running in the browser. That application makes small requests for data or processing from the host in a true client/server model.

The AJAX model is much closer to a thick client than a thin client. The primary difference from traditional fat client is that in AJAX you download the client program, or at the very least the definitions of the widget sand so on, for each page. With fat client the entire user interface is compiled into a program and then installed on the client.

Joe