Re: The "Presentation" Layer

I disagree ;)

By your definition, a function key on a 5250 is a request from the
user.

No i never said that. The client requests the terminal to display a screen and then waits until the terminal returns. A terminal may return for several reasons, e.g. the enter key is pressed, or a function key. The client program then resumes executing and does whatever it wants to do. For example it decides to refresh the data and display the same screen because the user has pressed F5.

Because the client program is in control it can do anything it wants. For example it can have a main loop which simply responds to "requests". That is, it displays a screen, and then acts on a "request" and again displays a screen. Like this, it functions more like a server, from an application architecture viewpoint. The program contains a bunch of procedures which randomly get called depending on the "request". And you may define a requests like "Enter", or "F5" etc. So in this case the procedures are "servers". The main loop however is still "client". And the main loop, of course, is the program.

Client/server roles are distributed over the software. Some parts have a server mrole, other client or both.

It's not about semantics. The client role and the server role are both distinct, well defined roles. No "semantics" here. But there may be some confusion because something can be a server or a client depending on which perspective you take.

Point is, no matter what kind of framework you use on the server or client to make life a bit easier, a browser is always a client which sends requests to the server. This is simply the way the web (HTTP) works.

The browser is not a slave to the server. From a programmers view using JSP you can maybe say the browser is a slave. But this is the role of the framework, to present an application architecture to the programmer where the browser acts like a slave, to keep things simple.

But in JSP Model 2, the browser acts as a slaved device
to the host application that is functionally equivalent to the 5250.

If you take the current page from the current browser and load it into another one (assuming all state is communicated with hidden variables and not cookies) you can simply push the SUBMIT button and it would work as if it was the original browser. This is a result of the browser being the client, and not a "slave".

Date: Fri, 18 Jul 2008 10:08:39 -0500
From: joepluta@xxxxxxxxxxxxxxxxx
To: web400@xxxxxxxxxxxx
Subject: Re: [WEB400] The "Presentation" Layer

john e wrote:

Joe,

Again, model 1 or 2, the servlet is a server program. It's not that you can simply start a servlet which then displays a page. The output of a servlet is always in response to an HTTP request.

In model 2 simply more of the application code (like what page to display next) resides on the server. But it's still client/server.

You said "the SUBMIT button on the JSP page returns to the calling servlet.". It does not return. A SUBMIT is a request. It is the beginning of a request-reponse cycle, not the end. The framework simply assures that the SUBMIT request is delegated to the same servlet that produced the page containing the SUBMIT.

By your definition, a function key on a 5250 is a request from the
user. In JSP Model 2 there is no functional difference between what the
browser does (display information from the host, allow user to enter
data, and then hit a button) and what the 5250 does (display information
from the host, allow user to enter data, and hit a function key).

Yes, the mechanics are different, and that's the disconnect between the
two approaches. But in JSP Model 2, the browser acts as a slaved device
to the host application that is functionally equivalent to the 5250.
But since the request is coming back to the servlet in response to the
page just displayed, the application architecture is sever/client.

If you disagree, that's cool. I'll just get out of the thread. I've
been doing this for too long to fight about semantics.

Joe
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