World Wide Web.

« browser does not display the URL for the user.

Instead, to indicate that an item is selectable, the browser changes the color of the item on the screen and keeps theURL associated with the link hidden.

When a user clicks on an item that corresponds to a selectable link, the browser consults the hidden information to find theappropriate URL, which the browser then follows to the selected page.

Because a link can point to any page in the Web, the links are known as hyperlinks.

See also Hypermedia. When a browser uses a URL to obtain a page, the information may be in one of many forms, including text, a graphical image, video, or audio.

Some Web pages areknown as active pages because the page contains a miniature computer program called a script or applet (a small application program).

When a script or applet arrives,the browser runs the program.

For example, a script can make images appear to move on the user's screen or can allow a user to interact with a mouse, keyboard, ormicrophone.

Active pages allow users to play games on the Web, search databases, or perform virtual scientific experiments.

Active pages are also used to generatemoving advertisements, such as a banner that keeps changing or a logo that appears to rotate. The codes that tell the browser on the client computer how to display a Web document correspond to a set of rules called Hypertext Markup Language (HTML).

An HTMLdocument consists of text with special instructions called tags, which are inserted to tell the browser how to display the text.

The HTML language specifies the exactrules for a document, including the meaning of each tag.

Thus, a person who creates an HTML page is responsible for inserting tags that cause the browser to displaythe page in the desired form.

Not all Web pages use HTML.

Graphics images are usually encoded using the Graphics Interchange Format (GIF) or Joint PhotographicExperts Group (JPEG) standards.

Active pages are written in a computer programming language such as ECMA Script or Java. IV WHO USES THE WEB Even though the World Wide Web is only one possible service that uses the Internet, surveys have shown that more than 80 percent of Internet traffic is for the Web.The percentage is likely to grow in the future. The most remarkable aspect of the World Wide Web arises from its broad appeal.

Users form a cross-section of society, including students preparing term papers,physicians researching the latest medical information, and college applicants investigating campuses or even filling out application and financial aid forms online.

Otherusers include investors examining the trading history of a company's stock or evaluating data on various commodities and mutual funds.

All the necessary information isavailable on the Web. Travelers investigating a possible trip can take virtual tours, check airline schedules and fares, and even book a flight on the Web.

Many destinations—including parks,cities, resorts, and hotels—have their own Web sites with guides and local maps.

Major delivery companies also have Web sites from which customers can trackshipments to determine the location of a package in transit or the time when it was delivered. Government agencies have Web sites where they post regulations, procedures, newsletters, and tax forms.

Many elected officials—including almost all members of theUnited States Congress—have Web sites, where they express their views, list their achievements, and invite input from the voters.

The Web also contains directories ofe-mail and postal mail addresses and phone numbers. Many merchants now do business on the Web.

Users can shop at the Web sites of major bookstores as well as clothing sellers and other retailers.

Many majornewspapers have special Web editions that are updated more frequently than the printed version.

In some cases, a Web site will offer basic information to everyone,but provide additional information to users who buy a subscription.

The major broadcast networks use the Web to provide supplementary materials for radio andtelevision shows, especially documentaries.

Electronic journals in almost every scholarly field are now on the Web.

Most museums now offer Web users a virtual tour oftheir exhibits and holdings.

Finally, many individuals have a Web site that describes their family, hobbies, and other personal information. V HISTORY The World Wide Web was developed by British physicist and computer scientist Timothy Berners-Lee as a project within the European Organization for Nuclear Research(CERN) in Geneva, Switzerland.

Berners-Lee combined several existing ideas into a single system to make it easier for physicists to use data on the Internet.

Mostimportant, he added multimedia—the ability to include graphics—to the hyperlink concept found in a previous Internet service known as gopher.

Berners-Lee had begunworking with hypertext in the early 1980s.

An early prototype implementation of the Web became operational at CERN in 1989, and the idea quickly spread touniversities in the rest of the world. Groups at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign researched and extended Web technology.

Theydeveloped the first browser that was used at many sites, named Mosaic, in 1993.

To allow the Web to be accessed from a wide variety of computer systems,researchers built multiple versions of Mosaic.

Each version was designed to be used with a specific operating system, the software that controls the computer.

Within ayear, computer programmer Marc Andreessen had formed a commercial company, Netscape Communications Corporation, to build and sell Web technologies. VI FUTURE TRENDS The amount of information on the Web continues to grow rapidly, as does the number of users around the world and the amount of online commerce.

For manybusinesses, the Web is replacing traditional catalog ordering.

In addition, people continue to extend and improve Web technology.

Several research efforts areunderway to generate new methods that search the Web for information, new methods for restricting access to intellectual property, and new technologies that willpermit live Webcasts similar to television broadcasts. Although most Web pages still use the HTML language, extensions and alternative technologies have been proposed.

The Extensible Markup Language (XML) isbecoming popular for business-to-business communication.

Unlike HTML, in which the meaning of all tags is pre-determined, XML allows companies that use it to definetheir own tags.

For example, a publisher and a bookstore might choose to define their own tags for information about authors, titles, and publication dates for theinformation they exchange.

Similarly, an automaker and a dealership might choose to define their own unique tags for models, body styles, and price.

XML definitionsare only meaningful to the parties involved.

For example, the automaker's software will not understand a book publisher’s author tag, and the bookstore's software willnot understand the automaker’s body style tag. Other alternative forms are also emerging.

The Wireless Markup Language (WML) is designed to be used with small wireless devices such as Web-enabled cell phones.Several scripting languages are available, including ECMA Script (which was originally called JavaScript) and Visual Basic.

Scripting is gaining importance as more sitesuse animation. Another Web technology expected to gain importance is known as a Content Distribution Network (CDN) or mirroring.

A CDN consists of multiple sites around the worldthat all contain the same information.

When a user requests a page, the CDN directs the request to the closest copy.

From a user's viewpoint, a CDN results in a fasterresponse.

From a company's viewpoint, a CDN is necessary because no single Web site can handle simultaneous requests from several hundred million users.

Thelargest Web sites already use CDN technology.. »