Re: The "Presentation" Layer

Agreed, a terminal is a "dumb" device. With "5250" i not only mean the terminal, but the whole "presentation technology", which is based on APPN. But the terminal part only implements a minimal set of functionality.

I was trying to explain that "5250" is radically different from the client/server approach used by web apps.

But in fact, there is no client/server here. From the application developers view anyway (and thats what counts). We simply have a program which happens to display on a remote terminal. The underlying technology is not important. However, from the point of view of the implementor of 5250 (in this case the app consists of the 5250 datastream, the firmware in the terminal and the display interface on the host), you could say that the program is a client and the terminal acts a server.

But from the applications programmer this is all irrelevant. No distinct client/server roles there, and that is the reason why this approach is so straightforward.

From: Jon.Paris@xxxxxxxxxxxxxx
To: web400@xxxxxxxxxxxx
Date: Fri, 18 Jul 2008 11:48:01 -0400
Subject: Re: [WEB400] The "Presentation" Layer

Let me ask this: What exactly makes 5250 peer-to-peer vs. client/
server? Is
it the "thin-ness" of the client (i.e. the terminal) ? Is it the
statefulness of the client in that it never loses connection and has a
direct line into the machine (brings back coaxial memories :-)?

Personally I find it misleading to think of 5250 as either peer-to-
peer OR client-server.

Would you describe the LCD display panel on the front of the "i" in
those terms? Or a printer? A 5250 is simply an output device. It
has no intelligence to speak of - everything is in the data stream and
is (theoretically) then subjected only to hardware/firmware
interpretation.

The fact that we now use emulators and can intercept and "webulate"
that data stream doesn't change the fundamental nature of the device.
The "state" information is retained by the driving program - the 5250
only knows when it has "permission to talk".

Maybe I'm being pedantic, but I think it confuses the debate when we
try to categorize 5250 in this way.

Jon Paris

www.Partner400.com
www.SystemiDeveloper.com


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