The World Wide Web ("WWW" or simply the "Web") is a global, read-write information space. Text documents, images, multimedia and many other items of information, referred to as resources, are identified by short, unique, global identifiers called Uniform Resource Identifiers (URIs) so that each can be found, accessed and cross-referenced in the simplest possible way.
The term is often mistakenly used as a synonym for the Internet itself, but the Web is actually something that is available over the Internet, just like e-mail and many other Internet services.
The World Wide Web is the combination of four basic ideas-
On the World Wide Web, a client program called a web browser retrieves information resources, such as web pages and other computer files, from web servers using their URLs and displays them, typically on a computer monitor. One can then follow hyperlinks in each page to other resources on the World Wide Web whose location is provided by these hyperlinks. It is also possible, for example by filling in and submitting web forms, to post information back to a web server for it to save or process in some way. The act of following hyperlinks is often called "browsing" or "surfing" the Web. Web pages are often arranged in collections of related material called "websites."
The phrase "surfing the Internet" was first popularized in print by Jean Armour Polly, a librarian, in an article called Surfing the INTERNET, published in the Wilson Library Bulletin in June, 1992. Although Polly may have developed the phrase independently, slightly earlier uses of similar terms have been found on the Usenet from 1991 and 1992, and some recollections claim it was also used verbally in the hacker community for a couple years before that. Polly is famous as "NetMom" in the history of the Internet.
For more information on the distinction between the World Wide Web and the Internet itself — as in everyday use the two are sometimes confused — see Dark internet where this is discussed in more detail.
Although the English word worldwide is normally written as one word (without a space or hyphen), the proper name World Wide Web and abbreviation WWW are now well-established even in formal English. The earliest references to the Web called it the WorldWideWeb (an example of computer programmers' fondness for CamelCase) or the World-Wide Web (with a hyphen, this version of the name is the closest to normal English usage).
Ironically, the abbreviation "WWW" is somewhat impractical as it contains three times as many syllables as the full term "World Wide Web", and thus takes longer to say; however it is easier to type
When a viewer wants to access a web page or other resource on the World Wide Web, he normally begins either by typing the URL of the page into his or her web browser, or by following a hypertext link to that page or resource. The first step, behind the scenes, is for the server-name part of the URL to be resolved into an IP address by the global, distributed Internet database known as the Domain name system or DNS.
The next step is for an HTTP request to be sent to the web server at that IP address, for the page required. In the case of a typical web page, the HTML text, graphics and any other files that form a part of the page will be requested and returned to the client (the web browser) in quick succession.
The web browser's job is then to render the page as described by the HTML, CSS and other files received, incorporating the images, links and other resources as necessary. This produces the on-screen 'page' that the viewer sees.
Most web pages will themselves contain hyperlinks to other relevant and informative pages and perhaps to downloads, source documents, definitions and other web resources.
Such a collection of useful, related resources, interconnected via hypertext links, is what has been dubbed a 'web' of information. Making it available on the Internet produced what Tim Berners-Lee first called the World Wide Web in the early 1990s [1] [2].1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
If the user returns to a page fairly soon, it is likely that the data will not be retrieved from the source web server, as above, again. By default, browsers cache all web resources on the local hard drive. An HTTP request will be sent by the browser that asks for the data only if it has been updated since the last download. If it has not, the cached version will be reused in the rendering step.
This is particularly valuable in reducing the amount of web traffic on the internet. The decision about expiry is made independently for each resource (image, stylesheet, JavaScript file etc, as well as for the HTML itself). Thus even on sites with highly dynamic content, many of the basic resources are only supplied once per session or less. It is worth any web site designer collecting all the CSS and JavaScript into a few site-wide files so that they can be downloaded into users' caches and reduce page download times and demands on the server.
There are other components of the internet that can cache web content. The most common in practice are often built into corporate and academic firewalls where they cache web resources requested by one user for the benefit of all.
Apart from the facilities built into web servers that can ascertain when physical files have been updated, it is possible for designers of dynamically generated web pages to control the HTTP headers sent back to requesting users, so that pages are not cached when they should not be — for example internet banking and news pages.
This helps with understanding the difference between the HTTP 'GET' and 'POST' verbs — data requested with a GET may be cached, if other conditions are met, whereas data obtained after POSTing information to the server usually will not.
The underlying ideas of the Web can be traced as far back as 1980, when Tim Berners-Lee, a Briton, built ENQUIRE (referring to Enquire Within Upon Everything, a book he recalled from his youth). While it was rather different from the Web we use today, it contained many of the same core ideas (and even some of the ideas of Berners-Lee's next project after the WWW, the Semantic Web).
In March 1989, Tim Berners-Lee wrote Information Management- A Proposal, which referenced ENQUIRE and described a more elaborate information management system. With help from Robert Cailliau, he published a more formal proposal for the World Wide Web on November 12, 1990.
A NeXTcube was used by Berners - Lee as the world's first web server and also to write the first web browser, WorldWideWeb in 1990.
By Christmas 1990, Berners-Lee had built all the tools necessary for a working Web [3]- the first Web browser (which was a Web editor as well), the first Web server and the first Web pages which described the project itself.
On August 6, 1991, he posted a short summary of the World Wide Web project on the alt.hypertext newsgroup. This date also marked the debut of the Web as a publicly available service on the Internet. The crucial underlying concept of hypertext originated with older projects from the 1960s, such as Ted Nelson's Project Xanadu and Douglas Engelbart's oN-Line System (NLS). Both Nelson and Engelbart were in turn inspired by Vannevar Bush's microfilm-based "memex," which was described in the 1945 essay "As We May Think".
Berners-Lee's breakthrough was to marry hypertext to the Internet. In his book Weaving The Web, he explains that he had repeatedly suggested that a marriage between the two technologies was possible to members of both technical communities, but when no one took up his invitation, he finally tackled the project himself. In the process, he developed a system of globally unique ide