Web Info 3
 
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More TRANSACTIONS
Our model for the Web transaction by which we get a file is:

  1. We request a document, say
    http://howard.nebrwesleyan.edu/index.html,
    which request is sent to a server, and
  2. The server sends it back to our computer, at which point
  3. The Web browser we're using (Netscape or Internet Explorer) displays it for us to see.

Forms
Suppose we do something a little more interesting: for example, suppose we are confronted by a Form, like the following:

Username:
Password:
In this case, when we press Submit button (the one labeled "log in"), we continue the transaction shown above. (Actually, we don't: this particular form does absolutely nothing. But, with a little imagination, we could conceive that it might...)
  1. Our Web browser sends the information in the form back to the server,
  2. the server does something with it (there's a computer program hiding behind this, really),
  3. and then it sends a new page back to our browser,
  4. which displays it just like before.

This type of transaction is server-side form processing, and requires that we have some program on the server to do the something. You will also hear that it uses CGI -- the "Common Gateway Interface" for the transaction.

One more form, and such
Ok, what about the following form elements?

 

 a:  b:  
 a + b =  
 
   
 
Change location to:
  
 

These are both done with client-side forms, in particular, code written in javascript. Javascript, along with the completely unrelated but very confusingly named java, as well as other completely unrelated but less confusingly named shockwave and other "plug-ins", allow us to make Web pages interactive. What does this mean? It means a transaction model:

  1. We interact with the Web page, and
  2. our browser interprets what we've done based on information in the Web page, and reacts accordingly.

Important Stuff
  • For normal text, image, movie, etc. files, our transaction model is
    request -> server response -> browser display.
  • When we have a server-side form, the model is
    request -> server response -> browser display ->
    browser response -> server process and reply -> browser display.
  • When we have a client-side processing, the model is
    request -> server response -> browser display ->
    user input -> browser process -> browser redisplay.
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Gavin's HHMI 02 Web Workshop: Web Info 3
Last Modified: Thu May 30 12:51:38 EDT 2002
Comments to glarose@umich.edu
©2002 Gavin LaRose, UM Math Dept