BOOK8-Unit3Inventorsandinventions-“江南联赛”一等奖

WorldWideWeb

WWW'shistoriclogodesignedbyRobertCailliau

TheWorldWideWeb(commonlyshortenedtotheWeb)isasystemofinterlinked,hypertextdocumentsaccessedviatheInternet.Withawebbrowser,auserviewswebpagesthatmaycontaintext,images,videos,andothermultimediaandnavigatesbetweenthemusinghyperlinks.TheWorldWideWebwascreatedin1989bySirTimBerners-LeeandSirSamWalkerfromtheUnitedKingdom,andRobertCailliaufromBelgium,workingatCERNinGeneva,Switzerland.Sincethen,Berners-Leehasplayedanactiveroleinguidingthedevelopmentofwebstandards(suchasthemarkuplanguagesinwhichwebpagesarecomposed),andinrecentyearshasadvocatedhisvisionofaSemanticWeb.

HowtheWebworks

ViewingawebpageontheWorldWideWebnormallybeginseitherbytypingtheURLofthepageintoawebbrowser,orbyfollowingahypertextlinktothatpageorresource.Thewebbrowserthenbeginsaseriesofcommunications,behindthescenes,inordertofetchanddisplayit.

First,theserver-nameportionoftheURLisresolvedintoanIPaddressusingtheglobal,distributedInternetdatabaseknownasthedomainnamesystem,orDNS.ThisIPaddressisnecessarytocontactandsenddatapacketstothewebserver.

ThebrowserthenrequeststheresourcebysendinganHTTPrequesttothewebserveratthatparticularaddress.Inthecaseofatypicalwebpage,theHTMLtextofthepageisrequestedfirstandparsedimmediatelybythewebbrowser,whichwillthenmakeadditionalrequestsforimagesandanyotherfilesthatformapartofthepage.Statisticsmeasuringawebsite'spopularityareusuallybasedonthenumberof'pageviews'orassociatedserver'hits',orfilerequests,whichtakeplace.

Havingreceivedtherequiredfilesfromthewebserver,thebrowserthenrendersthepageontothescreenasspecifiedbyitsHTML,CSS,andotherweblanguages.Anyimagesandotherresourcesareincorporatedtoproducetheon-screenwebpagethattheusersees.

Mostwebpageswillthemselvescontainhyperlinkstootherrelatedpagesandperhapstodownloads,sourcedocuments,definitionsandotherwebresources.Suchacollectionofuseful,relatedresources,interconnectedviahypertextlinks,iswhatwasdubbeda"web"ofinformation.MakingitavailableontheInternetcreatedwhatTimBerners-LeefirstcalledtheWorldWideWeb(notetheoriginalname'suseofCamelCase,subsequentlydiscarded)in1990.

Caching

Ifauserrevisitsawebpageafteronlyashortinterval,thepagedatamaynotneedtobere-obtainedfromthesourcewebserver.Almostallwebbrowserscacherecently-obtaineddata,usuallyonthelocalharddrive.HTTPrequestssentbyabrowserwillusuallyonlyaskfordatathathaschangedsincethelastdownload.Ifthelocally-cacheddataisstillcurrent,itwillbereused.

CachinghelpsreducetheamountofwebtrafficontheInternet.Thedecisionaboutexpirationcanbemadeindependentlyforeachdownloadedfile,whetherimage,stylesheet,JavaScript,HTML,orwhateverothercontentthesitemayprovide.Thusevenonsiteswithhighlydynamiccontent,manyofthebasicresourcesmayonlyneedtoberefreshedonceeveryfewsessions.WebsitedesignersmayfinditworthwhiletocollatesharedresourcessuchasCSSdataandJavaScriptintoafewsite-widefilessothattheycanbecachedefficiently.Thishelpsreducepagedownloadtimesandlowersdemandsonthewebserver.

ThereareothercomponentsoftheInternetthatcanalsocachewebcontent.Inpractice,themostwidely-usedcachesarebuiltintocorporateandacademicfirewallswhichcachewebresourcesrequestedbyoneuserforthebenefitofall.(SeealsoCachingproxyserver.)Somesearchengines,suchasGoogleorYahoo!,alsostorecachedcontentfromwebsites.

Apartfromthefacilitiesbuiltintowebserversthatcandeterminewhenfileshavebeenupdated,designersofdynamically-generatedwebpagescancontroltheHTTPheaderssentbacktorequestingusers,sothattransientorsensitivepagesarenotcached.Internetbankingandnewssitesfrequentlyusethesefacilities.

DatarequestedwithanHTTP'GET'islikelytobecachedifotherconditionsaremet,whereasdataobtainedviaa'POST'commandisassumedtobedependentonthedatathatwasPOSTedandsowillnotbecached.

History

ThisNeXTcubeusedbyBerners-LeeatCERNbecamethefirstWebserver.

Theconceptofahome-basedglobalinformationsystemgoesbackatleastasfarasIsaacAsimov'sshortstory"Anniversary"(AmazingStories,March1959),inwhichthecharacterslookupinformationonahomecomputercalleda"Multivacoutlet"--whichwasconnectedbya"plantewidenetworkofcircuits"toamile-long"super-computer"somewhereinthebowelsoftheEarth.OnecharacteristhinkingofinstallingaMulitvac,Jr.modelforhiskids.

Interestingly,thestorywassetinthefardistantfuturewhencommercialspacetravelwascommonplace,andyetthemachine"printstheansweronaslipoftape"thatcomesoutaslot--thereisnovideodisplay--andtheownerofthehomecomputersaysthathedoesn'tspendthekindofmoneytogetaMultivacoutletthattalks.

TheunderlyingideasoftheWebcanbetracedasfarbackas1980,when,atCERNinSwitzerland,TimBerners-LeebuiltENQUIRE(referringtoEnquireWithinUponEverything,abookherecalledfromhisyouth).Whileitwasratherdifferentfromthesysteminusetoday,itcontainedmanyofthesamecoreideas(andevensomeoftheideasofBerners-Lee'snextprojectaftertheWorldWideWeb,theSemanticWeb).

InMarch1989,TimBerners-Leewroteaproposal,whichreferencedENQUIREanddescribedamoreelaborateinformationmanagementsystem.WithhelpfromRobertCailliau,hepublishedamoreformalproposalfortheWorldWideWebonNovember12,1990.

ANeXTcubewasusedbyBerners-Leeastheworld'sfirstwebserverandalsotowritethefirstwebbrowser,WorldWideWeb,in1990.ByChristmas1990,Berners-LeehadbuiltallthetoolsnecessaryforaworkingWeb:thefirstwebbrowser(whichwasawebeditoraswell),thefirstwebserver,andthefirstwebpageswhichdescribedtheprojectitself.

OnAugust6,1991,hepostedashortsummaryoftheWorldWideWebprojectonthenewsgroup.ThisdatealsomarkedthedebutoftheWebasapubliclyavailableserviceontheInternet.

Thecrucialunderlyingconceptofhypertextoriginatedwitholderprojectsfromthe1960s,suchasTedNelson'sProjectXanaduandDouglasEngelbart'soN-LineSystem(NLS).BothNelsonandEngelbartwereinturninspiredbyVannevarBush'smicrofilm-based"memex,"whichwasdescribedinthe1945essay"AsWeMayThink."

Berners-Lee'sbreakthroughwastomarryhypertexttotheInternet.InhisbookWeavingTheWeb,heexplainsthathehadrepeatedlysuggestedthatamarriagebetweenthetwotechnologieswaspossibletomembersofbothtechnicalcommunities,butwhennoonetookuphisinvitation,hefinallytackledtheprojecthimself.Intheprocess,hedevelopedasystemofgloballyuniqueidentifiersforresourcesontheWebandelsewhere:theUniformResourceIdentifier.

TheWorldWideWebhadanumberofdifferencesfromotherhypertextsystemsthatwerethenavailable.TheWebrequiredonlyunidirectionallinksratherthanbidirectionalones.Thismadeitpossibleforsomeonetolinktoanotherresourcewithoutactionbytheownerofthatresource.Italsosignificantlyreducedthedifficultyofimplementingwebserversandbrowsers(incomparisontoearliersystems),butinturnpresentedthechronicproblemoflinkrot.UnlikepredecessorssuchasHyperCard,theWorldWideWebwasnon-proprietary,makingitpossibletodevelopserversandclientsindependentlyandtoaddextensionswithoutlicensingrestrictions.

OnApril30,1993,CERNannouncedthattheWorldWideWebwouldbefreetoanyone,withnofeesdue.ComingtwomonthsaftertheannouncementthattheGopherprotocolwasnolongerfreetouse,thisproducedarapidshiftawayfromGopherandtowardstheWeb.AnearlypopularwebbrowserwasViolaWWW,whichwasbaseduponHyperCard.

Scholarsgenerallyagree,however,thattheturningpointfortheWorldWideWebbeganwiththeintroductionoftheMosaicwebbrowserin1993,agraphicalbrowserdevelopedbyateamattheNationalCenterforSupercomputingApplicationsattheUniversityofIllinoisatUrbana-Champaign(NCSA-UIUC),ledbyMarcAndreessen.FundingforMosaiccamefromtheHigh-PerformanceComputingandCommunicationsInitiative,afundingprograminitiatedbythen-SenatorAlGore'sHighPerformanceComputingandCommunicationActof1991,alsoknownastheGoreBill.PriortothereleaseofMosaic,graphicswerenotcommonlymixedwithtextinwebpages,anditspopularitywaslessthanolderprotocolsinuseovertheInternet,suchasGopherandWideAreaInformationServers(WAIS).Mosaic'sgraphicaluserinterfaceallowedtheWebtobecome,byfar,themostpopularInternetprotocol.

Standards

ManyformalstandardsandothertechnicalspecificationsdefinetheoperationofdifferentaspectsoftheWorldWideWeb,theInternet,andcomputerinformationexchange.ManyofthedocumentsaretheworkoftheWorldWideWebConsortium(W3C),headedbyBerners-Lee,butsomeareproducedbytheInternetEngineeringTaskForce(IETF)andotherorganizations.

Usually,whenwebstandardsarediscussed,thefollowingpublicationsareseenasfoundational:

Recommendationsformarkuplanguages,especiallyHTMLandXHTML,fromtheW3C.Thesedefinethestructureandinterpretationofhypertextdocuments.

Recommendationsforstylesheets,especiallyCSS,fromtheW3C.

StandardsforECMAScript,JavaScript,fromEcmaInternational.

RecommendationsfortheDocumentObjectModel,fromW3C.

AdditionalpublicationsprovidedefinitionsofotheressentialtechnologiesfortheWorldWideWeb,including,butnotlimitedto,thefollowing:

UniformResourceIdentifier(URI),whichisauniversalsystemforreferencingresourcesontheInternet,suchashypertextdocumentsandimages.URIs,oftencalledURLs,aredefinedbytheIETF'sRFC3986/STD66:UniformResourceIdentifier(URI):GenericSyntax,aswellasitspredecessorsandnumerousURIscheme-definingRFCs;

HyperTextTransferProtocol(HTTP),especiallyasdefinedbyRFC2616:HTTP/andRFC2617:HTTPAuthentication,whichspecifyhowthebrowserandservercommunicatewitheachother.

JavaandJavaScript

AsignificantadvanceinWebtechnologywasSunMicrosystems'Javaplatform.Itenableswebpagestoembedsmallprograms(calledapplets)directlyintotheview.Theseappletsrunontheend-user'scomputer,providingaricheruserinterfacethansimplewebpages.Javaclient-sideappletsnevergainedthepopularitythatSunhadhopedforavarietyofreasons,includinglackofintegrationwithothercontent(appletswereconfinedtosmallboxeswithintherenderedpage)andthefactthatmanycomputersatthetimeweresuppliedtoenduserswithoutasuitablyinstalledJavaVirtualMachine,andsorequiredadownloadbytheuserbeforeappletswouldappear.AdobeFlashnowperformsmanyofthefunctionsthatwereoriginallyenvisionedforJavaapplets,includingtheplayingofvideocontent,animation,andsomerichUIfeatures.Javaitselfhasbecomemorewidelyusedasaplatformandlanguageforserver-sideandotherprogramming.

JavaScript,ontheotherhand,isascriptinglanguagethatwasinitiallydevelopedforusewithinwebpages.ThestandardizedversionisECMAScript.WhileitsnameissimilartoJava,JavaScriptwasdevelopedbyNetscapeandithasalmostnothingtodowithJava,although,likeJava,itssyntaxisderivedfromtheCprogramminglanguage.Inconjunctionwithawebpage'sDocumentObjectModel,JavaScripthasbecomeamuchmorepowerfultechnologythanitscreatorsoriginallyenvisioned.Themanipulationofapage'sDocumentObjectModelafterthepageisdeliveredtotheclienthasbeencalledDynamicHTML(DHTML),toemphasizeashiftawayfromstaticHTMLdisplays.

Insimplecases,alltheoptionalinformationandactionsavailableonaJavaScript-enhancedwebpagewillhavebeendownloadedwhenthepagewasfirstdelivered.Ajax("AsynchronousJavaScriptAndXML")isaJavaScript-basedtechnologythatprovidesamethodwherebypartswithinawebpagemaybeupdated,usingnewinformationobtainedoverthenetworkatalatertimeinresponsetouseractions.Thisallowsthepagetobemoreresponsive,interactiveandinteresting,withouttheuserhavingtowaitforwholereloads.AjaxisseenasanimportantaspectofwhatisbeingcalledWeb.ExamplesofAjaxtechniquescurrentlyinusecanbeseeninGmail,GoogleMaps,andotherdynamicwebapplications.

Publishingwebpages

Webpagesareavailabletoindividualsoutsidemassmedia.Inordertopublishawebpage,onedoesnothavetogothroughapublisherorothermediainstitution,andpotentialreaderscouldbefoundinallcornersoftheglobe.

Unlikebooksandotherdocuments,hypertextdoesnotneedtohavealinearorderfrombeginningtoend.Itisnotnecessarilybrokendownintothehierarchyofchapters,sections,subsections,andsoon.

ManydifferentkindsofinformationarenowavailableontheWeb,andforthosewhowishtoknowothersocieties,cultures,andpeoples,ithasbecomeeasier.Whentravelinginaforeigncountryoraremotetown,onemightbeabletofindsomeinformationabouttheplaceontheWeb,especiallyiftheplaceisinoneofthedevelopedcountries.Localnewspapers,governmentpublications,andothermaterialsareeasiertoaccess,andthereforethevarietyofinformationobtainablewiththesameeffortmaybesaidtohaveincreasedfortheusersoftheInternet.

Althoughsomewebsitesareavailableinmultiplelanguages,manyareinthelocallanguageonly.Additionally,notallsoftwaresupportsallspecialcharacters,andRTLlanguages.ThesefactorswouldchallengethenotionthattheWorldWideWebwillbringaunitytotheworld.

Theincreasedopportunitytopublishmaterialsiscertainlyobservableinthecountlesspersonalpages,aswellaspagesbyfamilies,smallshops,etc.,facilitatedbytheemergenceoffreewebhostingservices.

Statistics

Accordingtoa2001study,thereweremorethan550billiondocumentsontheWeb,mostlyinthe"invisibleweb",ordeepweb.A2002surveyof2,024millionwebpagesdeterminedthatbyfarthemostwebcontentwasinEnglish:%;nextwerepagesinGerman%),French%),andJapanese%).Amorerecentstudy,whichusedwebsearchesin75differentlanguagestosampletheWeb,determinedthattherewereoverbillionwebpagesinthepubliclyindexablewebasoftheendofJanuary2005.

Speedissues

FrustrationovercongestionissuesintheInternetinfrastructureandthehighlatencythatresultsinslowbrowsinghasledtoanalternative,pejorativenamefortheWorldWideWeb:theWorldWideWait.SpeedinguptheInternetisanongoingdiscussionovertheuseofpeeringandQoStechnologies.OthersolutionstoreducetheWorldWideWaitcanbefoundonW3C.

Standardguidelinesforidealwebresponsetimesare(Nielsen1999,page42):

second(onetenthofasecond).Idealresponsetime.Theuserdoesn'tsenseanyinterruption.

1second.Highestacceptableresponsetime.Downloadtimesabove1secondinterrupttheuserexperience.

10seconds.Unacceptableresponsetime.Theuserexperienceisinterruptedandtheuserislikelytoleavethesiteorsystem.

Thesenumbersareusefulforplanningservercapacity.

Linkrotandwebarchival

Overtime,manywebresourcespointedtobyhyperlinksdisappear,relocate,orarereplacedwithdifferentcontent.Thisphenomenonisreferredtoinsomecirclesas"linkrot"andthehyperlinksaffectedbyitareoftencalled"deadlinks".

TheephemeralnatureoftheWebhaspromptedmanyeffortstoarchivewebsites.TheInternetAr