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2 About The World-Wide Web


The World-Wide Web (which is often referred to as W3, the Web or, as used in this document, WWW) is a distributed multimedia hypertext system. What is meant by this?

Distributed: information on WWW may be located on computer systems around the world.

Multimedia: the information held on WWW can include text, graphics, sound and even video.

Hypertext: access to the information is available using hypertext techniques, which typically involve using a mouse to select highlighted phrases or images. Once a phrase or image is selected it can result in information being retrieved from around the world.

The World-Wide Web was initially developed by Tim Berners-Lee and Robert Cailliau of CERN Laboratories, Geneva to provide an infrastructure for particle physicists throughout Europe to share information. Since the physicists were located in various organisations and used a variety of computer systems and applications software (including various word processing and text markup programs for producing reports) the World-Wide Web was developed using the client-server architecture, which ensured cross-platform portability.

Client-Server Architecture

The World-Wide Web is based on the client-server architecture which is illustrated in Figure 2-1.

Figure 2-1 WWW Client-Server Architecture.

The end user accesses the World-Wide Web using a browser client, typically on a desktop machine such as a PC, Macintosh or Unix workstation. The client will display hypertext links in some manner, such as underlining the links. Selecting a link (by clicking a mouse button with a graphical client, typing the number following the link using a simple text-based client or using speech or foot pedals, for example, with browsers for disabled users) to send a request over the network (which could be a local network, a national network such as JANET, or over the global network which can be referred to as the Internet). The request is sent to a World-Wide Web server, which typically runs on a powerful computer system. The server will retrieve the file which has been requested and deliver it to the client.

Once the client has started to retrieve the file it can display it on the local machine. If the client cannot display the file (many clients, for example, cannot view video clips) the client can pass the file on to an external viewer which can process the file.

This is a very simple overview of the WWW client-server architecture. Many other features are available: for example the server could send a message to the client, saying that the user is not authorised to access the file. However an understanding of this model will help you to see how the WWW can develop.

Early Browsers

One of the first browsers to be developed was the CERN command line browser. This can be accessed by using the command:

telnet telnet.w3.org

from a computer system which runs the telnet software. An example of use of the CERN command line browser is illustrated below.

telnet telnet.w3.org

                 Welcome to the World-Wide Web

This is just one of many access points to the web, the universe of
information available over networks. To follow references, just type the
number then hit the return (enter) key.
The features you have by connecting to this telnet server are very
primitive compared to the features you have when you run a W3 "client"
program on your own computer. If you possibly can, please pick up a client
for your platform to reduce the load on this service and  experience the
web in its full splendor.
For more information, select by number:
A list of available W3 client programs[1]
Everything about the W3 project[2]
Places to start exploring[3]
The First International WWW Conference[4]
This telnet service is provided by the WWW team at the European Particle
Physics Laboratory known as CERN[5]
1-5, Up, Quit, or Help:
Figure 2-2 The CERN Command Line Browser.

Notice that in the CERN command line browser in order to select a hypertext link you need to type the number which follows the link.

The CERN command line browser is a very simple client. The first WWW browser was developed by Tim Berners-Lee, the father of the World-Wide Web, for the NeXT system. However the NeXT hardware was not a commercial success and is no longer manufactured. One of the earliest graphical browsers was the Viola client which was developed for the X windows environment. Viola is illustrated in Figure 2-3.

Figure 2-3 The Viola Client.

Notice that in the Viola client the hypertext links are identified by the use of underlining.

Growth In Popularity

As shown in Figure 2-4 use of the WWW has grown tremendously since 1993. This chart, which compares the growth of WWW with a simpler distributed information system known as Gopher, is available at the URL ftp://ftp.isoc.org/isoc/charts/networks-gifs (the term URL will be explained later in this chapter). Much of this growth in popularity was due to the release of browsers for the X Windows, PC and Macintosh environments by the National Center For Supercomputing Applications (NCSA) at the University of Illinois.

Figure 2-4 Growth In Popularity of WWW.

Since CERN's remit was research in particle physics the WWW development team realised that they needed to involve other organisations in WWW development work. The involvement of NCSA in the WWW development programme resulted in the NCSA Mosaic For X, which was released in early 1993. An illustration of a pre-release version of Mosaic For X is shown in Figure 2-5.

Figure 2-5 A Pre-release Version Of NCSA Mosaic For X.

As can be seen from Figure 1-5 NCSA Mosaic For X provides access to a number of types of resources, including WAIS, Gopher, FTP, Usenet, Hytelnet, TeXinfo, X.500 and Whois resources. NCSA Mosaic was developed by a group of programmers at NCSA led by Marc Andreessen. NCSA Mosaic For X became such a success because:

In November 1993 NCSA released versions of Mosaic for the Microsoft Windows and Apple Macintosh environment. These browsers, which are freely available to the academic community, provided access to WWW for people who did not have access to Unix and X-Windows systems.

Examples of Usage

A number of examples of how the World-Wide Web is currently being used are given below. These are just a few examples of the many thousands of WWW serices which are currently available.

Publishing Research Information

Figure 2-6 illustrates how CERN (the European Particle Physics Laboratory) makes its technical papers available on the World-Wide Web. The URL for the paper illustrated is http://www1.cern.ch/ALICE/ENGINEERING/engineering.html

Figure 2-6 Example of Scientific Information Held At CERN.

Campus Wide Information Systems

The Honolulu Community College Campus Wide Information System (CWIS) was the first multimedia CWIS on the World-Wide Web. The URL for this CWIS is http://www.hcc.hawaii.edu/

Figure 2-7 The Honolulu Community College CWIS.

Teaching Applications

The Globewide Network Academy (GNA) won a Best of the Web 1994 award for the Introduction to Object Oriented Programming Using C++ distributed teaching application. The URL for this application is
Figure 2-8 A Distributed Teaching Application.


The School of Computer Studies at the University of Leeds was one of the first departments to use the multimedia capabilities of WWW to market its courses to potential students. The URL for this application is http://agora.leeds.ac.uk/WWW/MSc/MSc_text/leeds.html

Figure 2-9 University of Leeds Prospectus Information.

Virtual Libraries

Many virtual libraries, art galleries and exhibitions are available on the World-Wide Web. One of the first was the Vatican exhibition. The URL for this virtual exhibition is http://sunsite.unc.edu/expo/vatican.exhibit/Vatican.exhibit.html

Figure 2-10 The Vatican Exhibition.

Commercialisation Of WWW

The World-Wide Web is increasingly being used by commercial companies. For example the URL for the Pizza Hut ordering service is http://www.pizzahut.com/

Figure 2-11 A Commercial Application On WWW.

Government Use Of WWW

The World-Wide Web is also being used by governmental agencies. For example the URL for the CCTA is http://www.open.gov.uk/

Figure 2-12 The CCTA Government Information Service.


The following terms are used in this document:

Browser: An interactive program which is used to access information held on the World-Wide Web.

Client: Often used as a synonym for browser. A client is the software which normally runs on the local desktop machine (such as a PC, Apple Macintosh or Unix workstation). The client sends requests to the server software.

Server: Software which is used to deliver information to a client. Note that this term can also refer to the computer system on which the server software is running.

URL: Uniform Resource Locator. Can be regarded as the address of a file on the World-Wide Web. It includes the protocol (rules) for retrieving the file, the domain (name) of the computer system on which the server software runs and the file name to be retrieved. For example the URL http://info.cern.ch/hypertext/WWW/TheProject.html uses the http protocol to retrieve the file TheProject.html in the directory hypertext/WWW from the computer called info.cern.ch

HTML: Hypertext Markup Language. The native language for documents held on the World-Wide Web. HTML is an SGML (Standard Generalised Markup Language) application.

HTTP: Hypertext Transport Protocol. The protocol (set of rules) used to define the communications between the client and WWW server software.

Note that these terms are, for reasons of clarity, in some cases over-simplified.

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