A Potted View of the Web Who where
A Potted View of the Web Who, where, when, why. Approximately. Lee Gillam Department of Computing
Key Milestones - some developments • ARPANET: c 1967, decentralized computer network (US Do. D) => INTERNET: c 1983, relying on TCP/IP as a means to split data into packets and route them to computers • Email: c 1972, software for ARPANET • Personal Computer (affordable? ): c 1980, Apple Lisa/Mac and IBM PC • SGML: c 1970; Hypertext: c 1987, Apple’s Hypercard • Web Browser: c 1990, Tim Berners-Lee then at CERN, the European Organization for Nuclear Research – Hypertext + Internet + PC to produce an information network enabling physicists are CERN to share experimental results – First webpage: http: //info. cern. ch/hypertext/WWW/The. Project. html,
Key Milestones - some developments • Browsers - TBL Browser called “World. Wide. Web”; Mosaic: 1993; Opera: 1994; Mozilla (Netscape): 1994; Internet Explorer: 1995 …. . IE, Firefox, Safari, …. • Web Servers - Apache, IIS, …. . • Search Engines - Alta. Vista, Google, MSN, …. . • Estimated size of the web: 125 m sites (July 2007); 88 m (July 2006). Google: ~5 bn pages (+/- 14 bn) in English. 2001, English about 68%; 35% by 2004. • What else? Video, Audio, IM, …. • What next? – Semantic Web - the machine-understandable web (TBL)
How does it work? • Using the Domain Name Servers (DNS) – A distributed database that converts names to addresses. Overall management by the Internet Corporation for Assigned Names and Numbers (ICANN). US, 1998. –http: //www. bbc. co. uk (= http: //www. bbc. tv) => http: //212. 58. 224. 116 (http: //212. 58. 224. 116: 80/) – Hypertext Transfer Protocol (HTTP): for moving information (HTML) around the web. – HTTP client establishes TCP connection to a port (usually 80) [Email is port 25]; HTTP server (program) responds with messages (e. g. 404 error) and data (HTML). – Country code top level domains (cc. TLD): Nominet for. uk (. gb); . tv = Tuvalu, an island in the Pacific. . com, . net, . eu, . travel, . org …. (g. TLD)
How does it work? • Think about a distributed telephone conversation 26 26 what? 26 days Full days or working days? • What do we assume?
How does it work? <p>? ? ? <para> An unknown or unexpected error has occurred. • Communication and commonality (standards) are vital (TCP/IP, HTTP, HTML…. ) …. . Machines are dumb …. . The Browser still has to present the (represented) information somehow.
How does it work? • HTML: Elements, Attributes and Values <a href=“http: //www. cs. surrey. ac. uk”>Surrey Computing</a> – Elements delimit: e. g. <a>, </a> – Elements are additionally specified by attributes, e. g. href – Values fill elements or attributes, e. g. http: //www. cs. surrey. ac. uk and Surrey Computing – Should have closure for elements (corresponding </ >) browsers can be forgiving
How does it work? • HTML: Elements, Attributes and Values – Elements and values are embedded, e. g. <h 1> Visit the <a href=“http: //www. cs. surrey. ac. uk”> Surrey Computing </a> Website </h 1> – 1[h 1 2[text, a 3[@href 4[text]4, text]3, text]2] 1.
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