COMPUTER NETWORKING:THE WORLD WIDE WEB

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THE WORLD WIDE WEB

Next to e-mail, the World Wide Web is perhaps the most popular application of the Internet. It is a worldwide connected system of databases containing structured, hypertext, multimedia information that can be retrieved from any computer connected to the Internet.

History

The idea and basic concept of the World Wide Web was invented in Switzerland. In the late 1980s, two engineers, Tim Berners-Lee from the United Kingdom and Robert Cailliau from Belgium, work- ing at CERN (the European Laboratory of Particle Physics) in Geneva, decided to develop a new communication system for Internet-based international collaboration for physicists. The idea became a reality in 1990, when the first version of HTTP (the Hypertext Transfer Protocol), HTML (the Hypertext Markup Language), and URL (the Universal Resource Locator) addressing scheme were introduced and implemented.

For the first three years of its life, the growth of the World Wide Web was quite slow. Only a few dozen web servers were set up, and the Web was used only for what it was originally invented for: scientific communication.

The growth rate of the Web began to accelerate significantly in the second half of 1993 after the introduction of the first portable, graphical web browser, X Mosaic. This was the first browser facil- itating the new Internet application, the Web, to spread rapidly and penetrate all over the world. The Web has become a general-purpose technology, today serving not only scientific but all kinds of communication and information presentation needs.

The commercialization of the Internet also started with the birth of the World Wide Web. Com- panies not previously interested in using the Internet suddenly discovered the new possibilities and became the most active driving force in the development of networking. The first version of Netscape, another important web browser, was released in October 1994. The World Wide Web (W3) Consor-

tium, formed in 1994, drives and leads the technological development and standardization processes of Web technology.

Main Features and Architecture

As mentioned above, the World Wide Web is a hypertext-based database system of multimedia content. It can be used for building either local or global information systems. It is interactive, which means that the information flow can be bidirectional (from the database to the user and from the user to the database). It integrates all the other traditional information system technologies, such as ftp, gopher (a predecessor of the WWW in organizing and displaying files on dedicated servers), and news.

The content of a Web database can be static or dynamic. Static information changes rarely (or perhaps never), while dynamic content can be generated directly preceding (or even parallel to) actual downloading.

The Web content is made available by web servers, and the information is retrieved through the use of web browsers. The more or less structured information is stored in web pages. These pages may refer to multimedia objects and other web pages, stored either locally or on other Web servers. Thus, the network of the Internet web servers forms a coherent, global information system. Never- theless, because the different segments of this global system have been created and are operated and maintained independently, there is no unified structure and layout. This fact may result in considerable difficulties in navigating the Web.

The Universal Resource Locator is a general addressing scheme that allows unambiguous refer- ence to any public object (or service), of any type, available on the Internet. It was originally invented for the Word Wide Web, but today URL addressing is used in many other Internet applications. Examples of different URLs include:

• http: / / www.bme.hu / index.html

• ftp: / / ftp.funet.fi /

• mailto:maray@fsz.bme.hu

HTTP and HTML

Hypertext Transfer Protocol (HTTP) is the application-level network protocol for transferring Web content between servers and clients. (Hypertext is a special database system of multimedia objects linked to each other.) HTTP uses the services of the TCP transport protocol. It transfers independently the objects (text, graphics, images, etc.), that build up a page. Together with each object, a special header is also passed. The header contains information about the type of the object, its size, its last modification time, and so on. HTTP also supports the use of proxy and cache servers. HTTP proxies are implemented in firewalls to pass HTTP traffic between the protected network and the Internet. Object caches are used to save bandwidth on overloaded lines and to speed up the retrieval process.

Hypertext Markup Language (HTML) is a document description language that was designed to create formatted, structured documents using hypertext technique (where links are associated to con- tent pieces of the document so that these links can be easily applied as references to other related documents).

As originally conceived, HTML focused on the structure of the document. Later it was improved to provide more formatting features. In spite of this evolution, HTML is still quite simple. An HTML text contains tags that serve as instructions for structuring, formatting, linking, and so on. Input forms and questionnaires can also be coded in HTML. A simple example of an HTML text is as follows:

Computer Networking-0027

Details about the syntax can be found in the titles related to multimedia and the World Wide Web in the References. The above example will be displayed by the browser like this:

Example

This is just a short HTML example, containing almost nothing.

Multimedia Elements

The World Wide Web is sometimes called a multimedia information system because Web databases may contain also multimedia objects. It is obvious that in a well-designed and formatted document page graphic information and images can be used in addition to text. Web technology allows the inclusion of sound and moving pictures as well. Web pages may also contain embedded programs (e.g., Javascript, a language for designing interactive WWW sites) and thus can have some built-in intelligence.

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