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1、Unit3Theworldonline文化背景HowWorldWideWebworksThetermsInternetandWorldWideWebareoftenusedinevery-dayspeechwithoutmuchdistinction.However,theInternetandtheWorldWideWebarenotoneandthesame.TheInternetisaglobaldatacommunicationssystem.Itisahardwareandsoftwareinfrastructu
2、rethatprovidesconnectivitybetweencomputers.Incontrast,theWebisoneoftheservicescommunicatedviatheInternet.Itisacollectionofinterconnecteddocumentsandotherresources,linkedbyhyperlinksandURLs.ViewingaWebpageontheWorldWideWebnormallybeginseitherbytypingtheURLofthepage
3、intoaWebbrowser,orbyfollowingahyperlinktothatpageorresource.TheWebbrowsertheninitiatesaseriesofcommunicationmessages,behindthescenes,inordertofetchanddisplayit.First,theserver-nameportionoftheURLisresolvedintoanIPaddressusingtheglobal,distributedInternetdatabasekn
4、ownasthedomainnamesystem,orDNS.ThisIPaddressisnecessarytocontactandsenddatapacketstotheWebserver.ThebrowserthenrequeststheresourcebysendinganHTTPrequesttotheWebserveratthatparticularaddress.InthecaseofatypicalWebpage,theHTMLtextofthepageisrequestedfirstandparsedim
5、mediatelybytheWebbrowser,whichwillthenmakeadditionalrequestsforimagesandanyotherfilesthatformapartofthepage.Statisticsmeasuringawebsite'spopularityareusuallybasedonthenumberof'pageviews'orassociatedserver'hits',orfilerequests,whichtakeplace.Havingreceivedtherequir
6、edfilesfromtheWebserver,thebrowserthenrendersthepageontothescreenasspecifiedbyitsHTML,CSS,andotherWeblanguages.Anyimagesandotherresourcesareincorporatedtoproducetheon-screenWebpagethattheusersees.MostWebpageswillthemselvescontainhyperlinkstootherrelatedpagesandper
7、hapstodownloads,sourcedocuments,definitionsandotherWebresources.Suchacollectionofuseful,relatedresources,interconnectedviahypertextlinks,iswhatwasdubbeda"web"ofinformation.MakingitavailableontheInternetcreatedwhatTimBerners-LeefirstcalledtheWorldWideWeb(initsorigi
8、nalCamelCase,whichwassubsequentlydiscarded)inNovember1990.
