How the Web works

servers
browsers
text
graphics

Links Blue and Red

Back button or menu

Helper applications and Plugins

Cache

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The World Wide Web (WWW or just the "web") uses a Client/Server model of information distribution. This is a fancy way of saying that the web browsers are "network friendly." That is, they don't tie up a connection between client (the browser program running on your computer) and the server (WWW server program) as a telephone call does. The browser program makes a request for a file to the server. The server sends the file and then frees up the connection (essentially, forgets about that browser). When the browser needs a new file, it makes another request which is replied to. Thus, the network is tied up for a minimal amount of time. The language that the browser and server use to make and reply to requests is called the HyperText Transport Protocol or http.

While Netscape is receiving a page from a server, the graphic in the upper right corner of the window will have stars streaking through it. There will be text in the bottom of the window telling you the percentage of the information that has been received by the browser. If the transfer of information is taking too long (or you just want to visit another page), click on the Stop button or press command-period. If you are receiving a page, you can use the window scroll bars to move down and read more of the page as it is being received. Be careful, however. If you are receiving page 1 and you click on a link to page 2, Netscape will stop receiving page 1 and go get page 2. Be sure that is what you want to do before clicking on a link while receiving another page.

The main type of information that is sent is text. The browser program is responsible for formatting the text and making it look nice on the client computer. For instance, the first line of this slide looks like this when it is sent from the server to the browser:

It comes out looking like this:

The browser is told to use the biggest font size (H1) in a good looking font and, by the way, put in a return (p) after you display the words.

Graphics are sent and most browsers can view the two major formats. These formats are GIF (Graphical Interchange Format) and JPEG (Joint Photographic Experts Group). The compression technique used in the GIF format is patented by Unisys but used when CompuServe developed the format. In 1994, Unisys announced that they were going to charge a royalty for use of the format. A huge outcry on the net resulted in Unisys changing its policy and they do not charge for non-commercial, non-profit use on online services. GIF files preserve an image's quality while JPEG images are smaller, but do have some slight image loss.

The implementation of Hypertext on the web shows up as Links. These links are typically colored blue. When you click on a blue link, a request for another file is sent to a server on the net. This causes another page to appear. These links can be made to anywhere in the world. After you have taken a link, its color changes to red (or purple). Some browsers change the color of the links so that links that have just recently been taken are bright red, while older links taken are somewhere between blue and red (purplish). A tip in Netscape is if you put the cursor on top of a link, Netscape will show you where the link will go. You have to be able to interpret the URL (see next page) or link that it shows you on the bottom of the window.

As you might imagine, it's easy to get lost in Cyberspace following links helter-skelter. Most browsers build in mechanisms for keeping track of where you have been. The red or purplish links keep you from getting into an endless loop following links that you have already taken. Another mechanism is the Back button or menu. This is your "breadcrumb trail" through the woods. It keeps track of your path from the original page. However, it will only keep track of the very latest path. If you back up and go down another path, it only keeps that latest path. In addition to the Back button, you can jump back more than one page by selecting items from the Go menu.

Graphics, sound and movies can also be sent and included in the document. If the browser doesn't know how to display some data, it can call on other programs, called Helper Applications or Plugins. For instance, sound must be played by a Helper Application or a Plugin. A Plugin is a program that works within the browser. You don't have to leave Netscape to hear the sound. This is one way to extend the capabilities of the browser. New helpers can be written for new data types as they are created.

Another technique is used by many browsers to decrease network access and make the program run faster. They use a cache. A cache is a group of local files kept on the hard disk that are files that have been previously sent to the browser. When the user wants to return to one of those sites, the browser uses the local copy of the page on the hard disk, which loads much faster than requesting it over the network. You can force your browser to get a fresh copy of any page by using the Reload or Refresh button or menu item.

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