Friday, November 14, 2008

World Wide Web

In 1989, what has become the World Wide Web first entered the world in the mind of Tim Berners-Lee at CERN (Conseil Européenne pour la Recherche Nucleaire), the European Laboratory for Particle Physics near Geneva, Switzerland. The term World Wide Web wasn’t actually coined until 1990, when Tim BernersLee and Robert Cailliau submitted an official project proposal for developing the World Wide Web. The suggested a new way of sharing information between researchers at CERN who used different types of terminals and workstations. The unique aspect of their information sharing model was that the servers would host information and deliver it to clients in a device-independent form, and it would be the responsibility of each client to display (officially known as render) that information. Web clients and servers would communicate using a language (protocol) known as HTTP, which stands for the HyperText Transfer Protocol.

Hypertext is just text with embedded links to other text in it. The most common examples of hypertext outside of the World Wide Web are various types of online help files, where you navigate from one help topic to another by clicking on keywords or other highlighted text. The most basic form of hypertext used on the Web is HTML, the HyperText Markup Language.

On the World Wide Web, the servers are Web servers and the clients are typically browsers, such as Firefox, Opera, SeaMonkey, Netscape, Microsoft Internet Explorer, Apple’s Safari, and many others, running on your machine. To retrieve a Web page or other Web resource, you enter its address as a Uniform Resource Identifier (URI) in your browser by either typing it in or clicking on a link that contains a reference to that URI. Your browser contacts the appropriate Web server, which uses that URI to locate the resource that you requested and returns that resource as a stream of hypertext information that your browser displays appropriately, and you’re off and running!

Today’s browsers can understand many protocols beyond HTTP, including FTP (File Transfer Protocol, used to send and receive files), file (used to deliver plain-text files), POP (Post Office Protocol, used to send and receive electronic mail), and NNTP (Network News Transfer Protocol, used to send and receive Usenet News postings). Which protocol you use to retrieve a specific Web resource is encoded into the URI, and is referred to as a scheme in Web nerd terms. A URI specifies three basic things:

scheme://host/pathname

The scheme is one of http, ftp, file, and many more, and specifies how to contact the server running on host, which the Web server then uses to determine how to act on your request. The pathname is an optional part of the URI that identifies a location used by the server to locate or generate information to return to you. Web pages consist of a static or dynamically generated text document that can contain text, links to other Web pages or sites, embedded graphics in a variety of formats, references to included documents such as style sheets, and much more. These text documents are created using a structured markup language called HTML, the HyperText Markup Language. A structured markup language is a markup language that enforces a certain hierarchy where different elements of the document can appear only in certain contexts. Using a structured markup language can be useful to guarantee that, for example, a heading can never appear in the middle of a paragraph. Like documents in other modern markup languages, HTML documents consist of logical elements that identify the type of each element—it is the browser’s responsibility to identify each element and determine how to display (render) it. Using a device-independent markup language simplifies developing tools that render Web pages in different ways, convert the information in Web pages to other structured formats (and vice versa), and so on.

“Web addresses.” URL (Uniform Resource Locator) is the traditional acronym and term for a Web address, but the acronym and term URI (Uniform Resource Identifier) is actually more technically correct. Another acronym and term that you may come across is URN (Universal Resource Name). The relationship between these acronyms is the following: a URI is any way to identify a Web resource. A URL is a URI that explicitly provides the location of a resource and the protocol used to retrieve it. A URN is a URI that simply provides the name of a resource, and may or may not tell you how to retrieve it or where it is located.

Source of Information : Ubuntu Linux - Bible

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