How the Web Works - A Brief Introduction

Although we are ignoring a lot of details, you can picture the World Wide Web as working this way:

Now, the user (you, or a colleague or a customer) are at your workstation, which is probably running Windows, maybe Mac, or Linux

To get to the web, you get into your browser applicaiton, which is probably Microsoft Internet Explorer, Mozilla Firefox, Google Chrome, Apple Safari, or some other browser

You and the browser are considered the client

The "Web Server" has traditionally been a UNIX box; more recently it could be Windows box; now it can be a mainframe

The "Data server" has often been a mainframe running DB2 or a UNIX box with DB2 for UNIX or Oracle, Informix, or Sybase

With UNIX System Services available on the mainframe, the two separate systems, the Web server and the Data server, can now be consolidated to one box: the mainframe which runs your mission critical classic applications and at the same time it can run your new mission critical Web applications

Few people are aware of the fact that IBM ships a free Web Server along with z/OS, but it's there

A web page is just a text file stored on the Web server. This text is in a language called HTML (or possibly XHTML). That is, the words are stored along with formatting information, to tell the browser that something should be underlined, or bulleted, and so on

We say the browser renders the page

When you ask your browser to look at a web page (http://www...), the browser goes to the Web server, who finds the page and sends it back to the browser

The browser converts the text of HTML text into a visible web page on your workstation

If a web page has graphics or animations or music, these are all stored in separate files, and the HTML / XHTML just points to those files; they are sent along with the page file to your browser and the browser puts it all together

If the web page needs to accomplish something more sophisticated, it can actually ask for a program to be run, either on the workstation or on the web server

Programs that are run on the browser are either scripts (written in JavaScript, JScript, or similar languages) or "plugins" (support programs with their own processing abilities, such as Java, Macromedia Flash, and others)

Programs that are run on the server are called CGI (Common Gateway Interface) programs, or CGIs; a CGI is either a script (written in REXX, Java, shell script, and so on) or a program written in compiled languages (such as Assembler, COBOL, C, C++, PL/I, and others)

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