The 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 through the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia and navigate between them through hyperlinks.
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WWW Background
1989-1990 Tim Berners-Lee invents the World Wide Web at CERN
Means for transferring text and graphics simultaneously Client/Server data transfer protocol
Communication through application level protocol System ran on top of standard networking infrastructure
Text mark up language
Not invented by Bernes-Lee Simple and easy to use Requires a client application to render text/graphics
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WWW History contd.
1994 Mark Andreesen
First graphical browser Internets first killer app Freely distributed Became Netscape Inc.
1995 (approx.) Web traffic becomes dominant
Exponential growth E-commerce Web infrastructure companies World Wide Web Consortium
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WWW Components
Structural Components
Clients/browsers to dominant implementations Servers run on sophisticated hardware Caches many interesting implementations Internet the global infrastructure which facilitates data transfer
Semantic Components
Hyper Text Transfer Protocol (HTTP) Hyper Text Markup Language (HTML)
eXtensible Markup Language (XML)
Uniform Resource Identifiers (URIs)
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WWW Structure
Clients use browser application to send URIs through HTTP to servers requesting a Web page Web pages constructed using HTML (or other markup language) and consist of text, graphics, sounds plus embedded files Clients browser renders Web page returned by server
Page is written using Hyper Text Markup Language (HTML) Displaying text, graphics and sound in browser Writing data as well
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Uniform Resource Identifiers
Web resources need names/identifiers Uniform Resource Identifiers (URIs)
Resource can reside anywhere on the Internet
URI is the Uniform Resource Locator (URL)
Differences between URI and URL are beyond scope RFC 2396 (Generic Syntax)
Support for a wide range of popular languages Easy to add a new language for highlighting Highly customizable output formats
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HTTP Basics
Protocol for client/server communication
The heart of the Web Very simple request/response protocol
Client sends request message, server replies with response message
Stateless Relies on URI naming mechanism
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HTTP Request Messages
GET recover document specified by URL PUT store specified document under given URL HEAD recover info. about document specified by URL OPTIONS recover information about available options POST give information to the server DELETE remove document specified by URL
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HTML Basics
Hyper-Text Markup Language
A subset of Standardized General Markup Language (SGML) Facilitates a hyper-media environment
Embedded links to other documents and applications
Documents use elements to mark up or identify sections of text for different purposes or display characteristics Mark up elements are not seen by the user when page is displayed Documents are rendered by browsers
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