Re: The "Presentation" Layer -- WEB400

Joe wrote:

The entire page-at-a-time browser interface all the way up to JSP Model
2 has been server/client

I don't understand. Whether page-at-a-time or ajax, it's always client/server and not server/client because the browser always initiates the request. The browser is under control. The server responds to requests, whether this is with a complete page or simply some data.

Having all application code on the server and "nothing" (i.e. only HTML) on the client doesn't make it server/client. It's just that you're entire application is structured as functions that are executed as a result of the browser (client) making requests.

If the server outputs a complete page to the browser then this is a response to a request of the client. When done the server simply waits for the next request. This is different from server/client where the client program on the host is under control. It outputs a screen to the terminal whenever it wants to, not after receiving a request from the terminal.

Date: Fri, 18 Jul 2008 08:43:31 -0500
From: joepluta@xxxxxxxxxxxxxxxxx
To: web400@xxxxxxxxxxxx
Subject: Re: [WEB400] 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
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