20-03-2014, 12:00 PM
THE WORLD WIDE WEB (WWW)
WORLD WIDE WEB (.pptx (Size: 148.72 KB / Downloads: 11)
WWW Background
The web began in 1989 at CERN, the European center for neclear research.
The initial proposal for web of linked documents came from CERN physicist TIM Berners-Lee in March 1989.
Later, Marc Andreessen stared developing the first graphical browser, Mosaic.
In 1994, CERN and M.I.T. signed an agreement setting up the WORLD WIDW WEB CONSORTIUM(W3C), an organisation devoted to further developing the web, standarizing protocols, and encouraging interoperability between sites.
Architectural Overview
From user point of views ,the Web consists of a vast, worldwide collection of documents or web pages or just pages.
Each page may contain links to other pages anywhere in the world.
The idea of having one page point to another, now called HYPERTEXT.
Pages are viewed with a program called a browser.strings of text that are links to other pages, called HYPERLINKS,are often highlighted,by underlining,displaying them in a speacial color,or both.
To follow alink, user place the mouse cursor on the highlighted area ,which causes the cursor to change, and clicks on it.
If the user ever returns to the main pages,the links that have already been followed may be shown with a dotted underline to distinguish them from links that have not been followed.
The server side
The steps that a server perform in its main loop are:
Accept a TCP connection from a client (a browser).
Get the name of the file requested.
Get the file (from disk).
Return the file to the client.
Release the TCP connection.
Improvement to make server more efficient and the solution to the problem of accessing disk is to maintain a cache in memory of the n most recently used files. If the file is there it can be served directly.
Another method to make server faster is to make the server multithreaded. When a request comes in, the front end accepts it and builds a short record describing it . It then hands to one of the processing modules.
Statelessness and cookies
The web, on the other hand, is intrinsically stateless because each request for a new Web page is processed without any knowledge of previous pages requested. This is one of the chief drawbacks to the HTTP protocol. Because maintaining state is extremely useful, programmers have developed a number of techniques to add state to the World Wide Web, cookies is use one of them.
Web “cookies” are crucial to the convenience of the Internet. These small data files store passwords and user preferences and track users’ Internet movement, allowing for targeted and affiliate marketing. Cookies reflect the tension between ease-of-use and privacy found in online commerce.
XHTML (The eXtended HyperText Markup Language)
It is a family of XML markup languages that mirror or extend versions of the widely used Hypertext Markup Language (HTML), the language in which web pages are written.
While HTML (prior to HTML5) was defined as an application of Standard Generalized Markup Language (SGML), a very flexible markup language framework, XHTML is an application of XML, a more restrictive subset of SGML. Because XHTML documents need to be well-formed, they can be parsed using standard XML parsers—unlike HTML, which requires a lenient HTML-specific parser.