World Wide Web

I

Introduction

World Wide Web (WWW), computer-based network of information resources that combines text and multimedia. The information on the World Wide Web can be accessed and searched through the Internet, a global computer network. The World Wide Web is often referred to simply as “the Web”.

The Web started to become a popular resource after 1993 when the first widely distributed browser provided a convenient way to access a variety of information on the Internet. With the Web’s multimedia capabilities, users can read text, view pictures, watch animation, listen to sounds, and even explore interactive virtual environments. A user can move seamlessly from a document or Web page stored on the computer to a document or Web page stored on another computer.

The Web offers a place where companies, universities and other institutions, and individuals can display information about their products, services, facilities, or research, or their private lives. Only a small percentage of information on the Web is restricted to subscribers or other authorized users. The majority of Web pages are available to anyone who can access a computer that connects to the Internet. The Web has become a marketplace for many companies selling products or services, and a forum for people to exchange opinions and information. Museums, libraries, government agencies, and schools post information on the Web to make it available to others.

II

A Web of Computers

All communication on the Web is carried out among a set of computers that are interconnected by a computer network. Web technology can be used across an intranet (a network within a company or organization) or across the global Internet. As with all communications among computers, computers that comprise the Web employ two types of software: client and server (see Client/Server Architecture). To make information available, a computer runs a server program. To obtain and display information from a server, a computer user runs a client program. The client contacts a server to request information; the server responds by sending a copy of the requested information. To ensure that the exchange is meaningful, the client and server programs must follow a communication protocol, a set of rules that the two programs use to talk to one another. Like a language, a protocol specifies both the form and meaning of each possible message.

In principle, any computer can run a client or a server. In practice, however, large, powerful computers are usually chosen to run server software, and small personal computers (PCs) are sufficient to run client software. Powerful computers are chosen for server software because they must be able to handle requests for information from millions of people and do so quickly so that users who request information from the server will not experience long delays. PCs, however, are used by a single person to request a Web page. After a user makes a request, the user waits for the information to be displayed. Thus, the client program running on a user's computer only needs to handle one activity at a time. A server, however, must handle simultaneous requests from many clients, possibly millions.

The difference between the Web and the Internet is similar to the difference between a delivery service and a road system. The Internet corresponds to a road network that allows traffic to flow between destinations, and the Web corresponds to a service that uses the roads to move information from one place to another. Confusion about the difference between the Web and the Internet arose because the Web has become extremely popular and now accounts for the majority of Internet traffic. However, other services also use the Internet to carry their traffic. For example, the Internet's electronic mail (e-mail) service allows users to send and receive textual messages, and the file transfer service allows a user to transfer a copy of a file from one computer to another.

Although many services use the Internet to carry data from one computer to another, each service follows a separate set of rules that define the messages used in the exchange. The Web uses the HyperText Transfer Protocol (HTTP), electronic mail uses the Simple Mail Transfer Protocol (SMTP), and file transfer uses the File Transfer Protocol (FTP). The application programs that users run to access the Internet often involve a blurring of the distinction between these services. For example, an application program that can send e-mail also allows a user to transfer the contents of a file, and an application program used to access the Web also allows the user to process e-mail.

III

How the Web Works

To access the Web, a user must have a computer connected to the Internet and appropriate software. The connection between the user's computer and the Internet can consist of a permanent, dedicated connection or a temporary, dial-up connection. A dial-up connection uses a modem to send data over the telephone system to another modem. It offers the lowest cost but requires the user to wait for the connection to be established each time the modem is used. A permanent connection uses a technology such as Asymmetric Digital Subscriber Line (ADSL, also known as DSL), a cable modem, or a dedicated leased circuit. It remains in place and is ready to use at all times. Permanent Internet connections cost more but offer higher capacity—that is, they can send more data at a faster speed.

Two pieces of software are needed to access the Web: (1) basic communication software that a computer uses to transfer data across the Internet and (2) a Web application program known as a browser that can contact a website to obtain and display information. Basic communication software, which is usually built into the computer's operating system (the software that controls the computer), allows the computer to interact with the Internet. The software follows a set of protocol standards that are collectively known as TCP/IP (Transmission Control Protocol/Internet Protocol). TCP/IP software is built into the computer's operating system and thus remains hidden from users. The software is invoked automatically by application programs that use the Internet.

The second piece of software needed for Web access consists of an application program known as a Web browser. Unlike basic communication software, a browser is directly visible to the user. To access the Web, the user must invoke the browser and enter a request. The browser then acts as a client. The browser contacts a Web server, obtains the requested information, and displays the information for the user.

Information on the Web is divided into pages, each of which is assigned a short identification string that is known as a Uniform Resource Locator (URL). A URL encodes three pieces of information: the protocol a browser should use to obtain the item, the name of a computer on which the item is located, including its domain name, and the name of the item. The domain name can indicate whether the site is operated by a commercial business or a non-profit-making organization. For example, .com signifies a commercial site whereas .org was designated for use by non-profit-making organizations. Many other domain names exist, including .co.uk for websites relating to the United Kingdom, .edu for sites established by educational institutions, .info for information sites, and .biz for businesses.

Only the computer name is required in a URL. If the protocol is omitted, a browser assumes “http://”, and if the name of an item is omitted, the server chooses a page to send. Thus, the URL uk.encarta.msn.com, which consists only of a computer name, is also valid.

Before it can obtain information, a browser must be given a URL. A user can enter the URL manually or click on a selectable link. In each case, once it has been given a URL, the browser uses the URL to obtain a new page, which it then displays for the user. The URL associated with a selectable link is not usually visible. To indicate that an item is selectable, the browser changes the colour of the item on the screen and keeps the URL 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 the appropriate URL, which the browser then follows to the selected page. Links can point to any page on the Web and 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 are known 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, or microphone. Active pages allow users to play games on the Web, search databases, or perform virtual scientific experiments. Active pages are also used to generate moving 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 HTML document 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 exact rules for a document, including the meaning of each tag. Thus, a person who creates an HTML page is responsible for inserting tags that allow the browser to display the page in the desired form. Not all Web pages use HTML. Graphics images are usually encoded using the Graphics Interchange Format (GIF) or Joint Photographic Experts 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 of several possible services that may use the Internet, the vast majority of Internet traffic is for the Web. The most remarkable aspect of the World Wide Web arises from its broad appeal. Users form a cross-section of society, including students preparing essays, physicians researching the latest medical information, and university applicants investigating campuses or filling out application forms online. Other users include investors examining the trading history of a company's shares or evaluating data on commodities and unit trusts. All the necessary information is available on the Web.

Travellers investigating a prospective trip can take virtual tours, look up airline schedules and fares, and book flights on the Web. Many destinations—including parks, cities, resorts, and hotels—have their own websites with guides and local maps. Major delivery companies also have websites from which customers can track shipments to determine the location of a package in transit or the time when it was delivered.

Government agencies have websites where they post regulations, procedures, newsletters, and tax forms. It is common for elected officials, such as members of parliament, to have websites, where they express their views, list their achievements, and invite input from voters. The Web also contains directories of e-mail and postal addresses, and telephone numbers.

Many merchants now do business on the Web. Users can shop at the websites of book shops as well as clothing sellers and other retailers. Major newspapers have special Web editions. In some cases, a website will offer basic information to everyone, but provide additional information to users who buy a subscription. Broadcasters use the Web to provide supplementary materials for radio and television programmes. Electronic journals in most academic fields are now available on the Web, while museums offer Web users virtual tours of their exhibits and collections. Also, many individuals now have a website that describes their family, hobbies, and other personal information.