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1、Chapter9BrowsersandsearchenginesHowdatacanbeextractedfromtheWebinanastonishinglyshorttime,with-outanycertaintythatwhatwegetiswhatweactuallywanted.Whentheetwork" rstappearedattheendofthe1960s,onlyasmallcliqueofexpertscoulduseit.ARPANEThadbeendesignedbyke
2、enschol-arsasamilitaryandresearchtool,withouttheintentionofiteverbe-comingavehicle(perhapsthevehicle)forcommercialbusiness.Andevenafterthetransitionofthe1980swhenARPANETandotherexistingnet-worksstartedoperatingtogetherundertheTCP/IPprotocolgivingrisetothe
3、Internet,thenetworkwasstillnotsuitableforthegeneralpublic.ThekillerideawasthecreationoftheWeb,withthecrucialfeatureofassign-ingaUniformResourceLocator(URL)toeachWebpage,forexample:http://en.wikipedia.org/wiki/URL-theWikipediapageaboutURLs.Buteventhen,wand
4、eringintheevergrowingWebwashardfornonspecialists,alittlelikenavigatinganoceanwithoutGPSorevenacompass.1AgreatimprovementinInternetusagecamewiththedevelopmentofbrowsersthatpermitanyWebpagetobeviewedonceitsURLisknown.Thesearchcanstartfromagivenorpreviouslyk
5、nownsite,andproceedfollowingclickablelinksuntiladesiredoratleastinterestingpageisreached.ItgoeswithoutsayingthatmostoftherelevantinformationontheInternetremainsunreach-ableifonecanonlyuseabrowserinthisway,butthebigleaptowardstheconsumerInternetrevolutionh
6、adbeentaken.The rstpopularbrowserwasNetscapeNavigator,developedfromtheearlierprototypeMosaicproducedbytheUniversityofIllinoisandreleasedfreelytonon-commercialusersattheendof1994.Comparedtoearliersoft-ware,themajorinnovationofthisnewbrowserwasthatitallowed
7、on-the-
ydisplayofwebpages,afeatureofgreatimportanceatthetimebecausecon-nectionspeedwasgenerallyverylimited.Ausercouldstartreadingapageinsecondsaslongasaportionofdatahadarrived,withoutwaitingforthefullloadingofthepage.Graphicscouldbemadetoloadlast.TheNets
8、capebrowserwascompatiblewithmostoperatingsystemsandremainedthetech-1ThisanalogymayexplaintheproliferationofdeceptivemarinetermsonWebsearchinglikenavigation,sur ng,crawling(ifweconsideritamethodofswimming):alloperati
