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CGI
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HTML has come a long way since it was first created, giving Web designers more graphical layout options. However, HTML by itself provides almost no interactivity beyond the ability to "jump" between sections of a document or from one page to another.
Nevertheless, there are ways to turn a static site into a dynamic one, enabling visitors to do a number of useful things. For example, readers can search for information in a database or select several items from a form and get a customized reply. One way to accomplish this type of interactivity is by using a Common Gateway Interface script, commonly known as a CGI or gateway script.
Common Gateway Interface (CGI)
Simply put, a gateway script is a program that runs on a web server and is triggered by input from a browser. The script is usually a link between the server and some other program running on the system, like a database. Most of the work happens on the server, behind the scenes. You only witness the result. The beauty of CGI is that it allows this sort of two-way communication through the use of HTML.
Page counter The front end of the web page, then, is programmed in HTML, and the gateway script usually is written in a programming language like C or Perl. Gateway scripts can be used for a wide variety of Web applications, ranging from the very simple to the complex. For example, a simple CGI script can track the number of visitors with a page counter or it might automatically update each page with the current time and date.
Image Map The most common use of CGI scripts is for implementing image maps and forms. An image map is a graphic image with distinct areas that have different URLs associated with each one. A gateway script for an image map keeps a list of the coordinates associated with the URLs. When you click on a particular region of the image, the browser feeds the coordinates to the server, which uses a script to locate the correct URL and return the appropriate HTML page to the browser.
Flash
Another widely used tool is a product called Flash from Macromedia, Inc. Flash is an animation and authoring program specifically developed for use on the Web. Viewing Flash animations requires a plug-in, a software program specifically designed to work with an existing program, i.e., a web browser. Flash plugs in to your web browser and plays animations embedded on a web page, in real-time.
Both Internet Explorer and Netscape Navigator support Flash and recent versions come bundled with the plug-in. If you don't already have it, you can download it from the Macromedia website. Once you've installed the plug-in, visit the rapidly growing list of Flash sites.
Java
Although Flash represents another milestone for the World Wide Web, the real breakthrough in interactivity and multimedia content delivery is a programming language called Java. Developed by Sun Microsystems, Inc., this powerful object-oriented programming language uses a Java-enabled web browser to run interactive applications.
Like a gateway script, Java is activated by a special HTML tag. Unlike gateway scripts, which require information on the server to run applications or process input, Java enables developers to create content that can be delivered to and run by users on their computers. This software supports anything that programmers can dream up, from spreadsheets and tutorials to interactive games and animation.
A well-done Java application on a single web page can engage a user for a long time. Rather than just providing text, sound, images, or videos to observe, a Java page offers a place to play, learn, or communicate and interact with others in a way that isn't necessarily based on going somewhere else on the Web through hyperlinks. In this way, Java turns the Web into a software delivery system in which users have things to do rather than just places to go. This offers the potential to transform the surfing behavior of Web users into one of playing and learning in interactive environments.
How does it work? Java makes Java browsers "smart" enough to interpret and execute the content, instead of relying on servers to provide information and functionality. When downloading a web page that contains the special hypertext tag called "APP," the Java browser knows that a special kind of Java program called an applet is associated with that page. The browser then downloads a file of information that describes the execution of that applet. This file of information is written in what are called bytecodes. The Java browser interprets these bytecodes and runs them as an executable program on the user's computer. All of this downloading and execution happens automatically. When a Java browser requests a web page, here's what happens:
- The HTML document is returned to the user's browser. The document contains the APP tag, which identifies the applet.
- The corresponding applet bytecode is transferred to the user's computer. This bytecode had been previously created by a Java compiler using the Java source code file for that applet.
- The Java browser on the user's host interprets the bytecodes and provides the display.
- The user may have further interaction with the applet without further downloading from the provider's web server. This is because the bytecode contains all of the information necessary to interpret the applet. So now, instead of the server computing a result, the Java browser becomes the mechanism for computation.
Good luck with your new website!
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