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26 Cards in this Set
- Front
- Back
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hypertext |
- text with links - allows free association - more creative learning - vannevar bush, first person to come up with hypertext. 1945 essay describing, among others, the memex system - ted nelson, 1960 Xanadu project, first computer hypertext system (bidirectional link. but there were too many rules) - tim burners-lee, 1989 starts the WWW project at CERN |
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multimedia |
- the integration of many forms of media - text -images -sound -animation |
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hypermedia |
- the combination of hypertext and multimedia - links are made between any media |
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the WWW project - background - aims - proposal |
background: cern - many networks existed - each network had many documents aims: - access documents from any network in seemless manner - worldwide (distributed) - easy to add documents (dynamic) proposal: - use hypertext - no intention to support hypermedia - research only |
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evolution of the web |
1989: tim burnes-lee begins work on the www project 1991: www operation at cern 1992: www goes public 1993: mosaic created by Marc Andreessen (first GUI browser) 1994: US senate allow commerce on internet 1994: netscape communications forms. Yahoo formed. 1995: microsoft internet explorer 1998: netscape became open source, developed into mozilla. google founded 1991-2001: "dotcom" boom and bust 2002-on: the web becomes obiquitous |
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HTTP |
-hypertext transfer protocol - language used to transfer hypertext documents - client server model |
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WWW |
- global body of information available using HTTP |
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cyberspace addresses |
uniform resource locations (URL) - address used for any web resources protocol - name of the protocol used (ftp://, http://, https://) domain - name of host computer e.g. www.cs.auckland.ac.nz file/resource - path of the file e.g. /~yusing/index.html |
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website |
a collection of webpages related to a single topic or theme. normally designed and maintained by a single individual or organization |
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webpages |
a hypermedia document designed for the www |
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web browser |
- software used to access information on the www - sends requests to a web server - client |
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web server |
- software that makes local files available through the web - fulfills requests from a web browser - server |
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accessing a webpage step 1 to step 3 |
step 1: client (web browser) runs on the local machine. - user requests a webpage - client contacts DNS to find the IP address webpage requested --> browser --> computer <---> DNS step 2 web server runs on the destination machine - request sent to destination domain - web server accepts the request and finds the web page - web page requested destination domain using HTTP browser --> computer ---> computer --> web server --> web page step 3 web page is sent from the server to the client - client displays the page - web page sent from server to client using HTTP web page <-- browser --< computer <--- computer <-- web server <-- web page |
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proxy |
a computer which sits between the client and server, intercepts and processes requests |
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cache |
store of information for quick access |
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firewall |
prevents unauthorised access to or from a private network |
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logging web page access |
client keeps log - history in browser operation system keeps log - requests are logged by windows on local machine ISP keeps log - requests from "IP address" to "IP address" for "page name" - some ISPs may have the logs available for users to check web server keeps log - gets request from "IP address" for "page name" |
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finding information |
- lots of users have problem finding new information - lots of users have problem finding known information. - webpage is very large, rapidly changing |
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search engines |
- automated - essential - our gateway to information |
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problems with the structure of web pages |
broken links - pages which have been moved - referring page is not altered no inherent security / tracking / accounting system - difficult to have layers of security - forces publishers to rely on advertising revenue no inherent information indexing - much of the information is not accessed by search engines - information created on-the-fly from databases - information in other formats |
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search engines |
- baidu - bing - yahoo |
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automatically search every webpage |
- archive contents - index all the words - try to determine the relevance of title page |
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can we trust the search engines? |
search engines - gateway to information - page are related - since ranking algorithms are secret, we have to trust publishers / advertisers - trick the search engines - search engines tailor adverts to searches - pay for a higher rating? - who owns the search engines? - how do they make their money? censorship - right-to-forget int he EU since june 2014 - but even before that, many requests for deletion |
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crawling the web |
- a web crawler is an internet bot that systematically browses the www and indexes encountered websites - might store encountered websites for later processing - start off with a list of URL and add any links encountered on these pages to their 'to-visit' list - follows a number of policies |
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google news |
- news aggreator, variation of the search engine - automatically searches thousands of publications and displays summaries -many unhappy |
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other online innovations |
- voice over IP - peer to peer networks - wolfram - free books - internet for everyone everywhere |
