World wide web

World Wide Web


The World Wide Web (abbreviated as WWW or W3, and commonly known as the Web) is a system of interlinked hypertext documents accessed via the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia, and navigate between them via hyperlinks.


Using concepts from his earlier hypertext systems like ENQUIRE,British engineer and computer scientist Sir Tim Berners-Lee, now Director of the World Wide Web Consortium (W3C), wrote a proposal in March 1989 for what would eventually become the World Wide Web. At CERN, a European research organization near Geneva situated on Swiss and French soil, Berners-Lee and Belgian computer scientist Robert Cailliau proposed in 1990 to use hypertext "... to link andaccess information of various kinds as a web of nodes in which the user can browse at will", and they publicly introduced the project in December.


Function


The terms Internet and World Wide Web are often used in everyday speech without much distinction. However, the Internet and the World Wide Web are not one and the same. The Internet is a global system of interconnectedcomputer networks. In contrast, the Web is one of the services that runs on the Internet. It is a collection of text documents and other resources, linked by hyperlinks and URLs, usually accessed by web browsers from web servers. In short, the Web can be thought of as an application "running" on the Internet.


Viewing a web page on the World Wide Web normally begins either by typing the URL ofthe page into a web browser or by following a hyperlink to that page or resource. The web browser then initiates a series of communication messages, behind the scenes, in order to fetch and display it. As an example, consider accessing a page with the URL http://example.org/wiki/World_Wide_Web.


First, the browser resolves the server-name portion of the URL (example.org) into an InternetProtocol address using the globally distributed database known as the Domain Name System (DNS); this lookup returns an IP address such as 208.80.152.2. The browser then requests the resource by sending an HTTP request across the Internet to the computer at that particular address. It makes the request to a particular application port in the underlying Internet Protocol Suite so that the computerreceiving the request can distinguish an HTTP request from other network protocols it may be servicing such as e-mail delivery; the HTTP protocol normally uses port 80. The content of the HTTP request can be as simple as the two lines of text.


WWW prefix


Many domain names used for the World Wide Web begin with www because of the long-standing practice of naming Internet hosts(servers) according to the services they provide. The hostname for a web server is often www, in the same way that it may be ftp for an FTP server, and news or nntp for a USENET news server. These host names appear as Domain Name System (DNS) subdomain names, as in www.example.com. The use of 'www' as a subdomain name is not required by any technical or policy standard; indeed, the first ever webserver was called nxoc01.cern.ch, and many web sites exist without it. According to Paolo Palazzi, who worked at CERN along with Tim Berners-Lee, the popular use of 'www' subdomain was accidental; the World Wide Web project page was intended to be published at www.cern.ch while info.cern.ch was intended to be the CERN home page, however the dns records were never switched, and the practice ofprepending 'www' to an institution's website domain name was subsequently copied. Many established websites still use 'www', or they invent other subdomain names such as 'www2', 'secure', etc. Many such web servers are set up such that both the domain root (e.g., example.com) and the www subdomain (e.g., www.example.com) refer to the same site; others require one form or the other, or they may map...