可扩展性标记语言XML中英文资料外文翻译文献.docx

可扩展性标记语言XML中英文资料外文翻译文献.docx

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可扩展性标记语言XML中英文资料外文翻译文献

可扩展性标记语言XML中英文资料外文翻译文献

UnderstandingtheExtensibleMarkupLanguage（XML）

ThisappendixtakesalookattheExtensibleMarkupLanguage（XML）—asuperbstructureddocumentformatstandardthatbusinessesareusingtoexchangebusinessdata.XMLcomplementsEJBnicelyaswell;infact,theEJB1.1specificationusesXMLasadocumentformatfordeploymentdescriptors.

Byreadingthisappendix,youwilllearnthefollowing:

■■WhybusinessesneedXML■■ThecoreconceptsbehindXMLprogramming■■HowEJBandXMLarerelated（whichwe’llexpanduponinAppendixD,coveringEJB1.1）XMLisanextremelyimportanttechnologyfortheInternet,anditisdestinedtobecomethede-factostandardforstructuringdocumentcontent.IfyoualreadyknowXML,feelfreetoskiptothesecondhalfofthisappendix,wherewediscusshowXMLandEJBarerelated.Otherwise,readon,andwewillexplainXMLfromtheground-up.ThisappendixexplainsenoughXMLforyoutobeginprogrammingwithEJB1.1.ForafulltourofXML,seethebook’saccompanyingWebsiteforlinkstoexternalresources.

BusinessNeedsforXMLWebeginbystudyingtheneedsofthebusinesscommunitythatmakeXMLsuchausefulstandard.WhyisXMLimportant?

Whatbusinessproblemsdoesitsolve?

WhydidweneedtocreateXMLratherthanuseexistingtechnology?

Thosearethequestionswewillanswerinthissection.ElectronicCommerceThebusinessneedforastandardsuchasXMLhasarisenwiththeadventofelectroniccommerce（alsocallede-commerce,e-business,oryourfavoritebuzzword）.Whenmostpeopleheartheword“electroniccommerce”,theyusuallythinkofWebstorefrontsthatyoucanvisittopurchasegoodselectronically.Thisiscalledbusiness-to-consumere-commercebecauseabusinessisconductingatransactionwithaconsumer.Examplesofbusiness-to-consumerWebsitesareA（）,B（）,andcarO（www.carO）.Bute-commerceextendsbeyondsimplythebusiness-to-consumermodel.Forinstance,anonlineauctionhousesuchaseBay（）facilitatestrans-actionsbetweenconsumersbyhostingauctions.Thisiscalledconsumer-to-consumere-commercebecausegoodsareexchanginghandsbetweenconsumers.Abusinessmayalsosellgoodstootherbusinessesandtakeconsumersoutofthepicturealtogether.Thiseconomicmodeliscalledbusiness-to-businesse-commerce,andiswheremostofthemoneychangeshandsbyfar,becauseeverybusinessneedstoconductinter-businesstransactionstosurvive.Manufacturersneedtobuypartsfromsuppliers.Resellersneedtobuyproductsfrommanufacturers.Andallcorporationsneedtobuyofficesuppliesandfurniture.Geographicallydistributedcompanies,conglomeratesandevenwholeindustries（suchasaerospace）relyoncommunication,andtheabilitytodistributemanufacturingactivitiesgivessomecompaniesanessentialeconomicadvantage.Business-to-businesse-commerceisthesinglelargestfinancialimpacttheInternetismakingontheworldeconomy,andhasbeenestimatedtobe20timesaslargeastheotherInterneteconomicmodels.Aswewillsee,business-to-businesse-commerceiswhereXMLhasthelargestimpactaswell.InadequacieswithExistingTechnologyThechallengeforbusinessestoconductaffairselectronicallyisforbusinessestounderstandeachother’sdata,suchasproducts,customers,andfinancialdata.Withapaper-basedsystem,ahumanbeingalwaysintervenedandcouldmakeGobacktothefirstpageforaquicklinktobuythisbookonline!

logicalguessesaboutambiguousdata.Withelectronicbusiness,however,computerprogramsneedtoreceiveaccurate,structureddata,ormillionsofdollarscouldbelostduetoincorrecttransactions.

Thus,astructureddatadocumentstandardisneededthatbusinessescanusetoshareinformation.Thisdocumentstandardshouldbesimpleenoughforanyonetouseelegantly,yetbepowerfulenoughtorepresentanybusinessdata.Acomputerprogramshouldbeabletoreadanelectronicdocumentstructuredinthislanguageandfigureoutthesemanticdetailsofthedocumentbasedonitsstructure.Forexample,anapplicationshouldbeabletoqueryadigitalpurchaseorderdocumentanddeterminewhatproductandquantitythepurchaseorderisfor.Let’stakealookattheexistingtechnologystandardsandexaminewhytheyareinadequateforourneeds.VANsandEDIElectronicbusinessisnotanewconcept.Companieshavealreadybeendoingitforyearsinaveryproprietaryway.BeforetheInternethitmainstream,twocorporationswouldconductbusinesselectronicallyusingathird-partyvendor’svalue-addednetwork（VAN）,orprivatenetworkthatlinkscompaniestogether.ThelargestfourVANvendorsareGeneralElectricInformationServices,IBMGlobalInformationNetwork,SterlingCommerce,Inc.,andHarbingerCorporation.ThestandardforconductingbusinessoverVANsiscalledElectronicDataEx-change（EDI）,astandardforfacilitatingtheelectronicexchangeofdata.EDIhastraditionallybeenusedoverVANsalthoughitisbeenextendedtorunovertheInternetaswell.EDIhaswidespreaduseinmultipleverticalindustries,fromthebusinesssector（transferringbusinessdocuments）totheeducationalsector（transferringstudentrecords,transcripts,andtestscores）.TheproblemswithVANsandEDIareasfollows:

■■VANsusingEDIareaveryexpensivesubscriptionservice,andchargebusinessesoutrageouspertransactionfees.■■VANsareachallengetolinktootherbusinessesthatarealreadyontheInternet.■■VANsaredesignedforbatch-modeprocessing（ratherthanjust-in-timeprocessing,whichisnecessaryforefficienttransactions）.■■Withinindustries,largecompaniestypicallydefineasetofEDItemplatesthatlockothercompaniesintoproprietarystandardsfordataexchange.

■■EDIisanoutdated,cumbersome,andnon-extensibleformatfortransferringdata.NotethatthereisdefinitelyalottobesaidaboutVANsandEDI.Manybusinessesrunquitesmoothlyonthesetechnologiestoday,asVANsusingEDIarequitereliableandsecure.Manycorporationsarealsoveryconcernedaboutgamblingtheirbusinessesonanythingnew.Duetothesefactors,plustheslowrateoftechnologyadoption,theEDImarketisgrowingrapidlyaswespeak.Inthelongrun,though,VANsandEDIarelikelytodieoffinfavorofnewertechnologyevolutions.WhatwouldyoudotoreplaceVANsandEDIwithanInternet-basedmodel?

FirstyouwouldneedtoreplacetheproprietaryVANnetworkswithanInternetlink.That’ssimplyahardwareproblem.ThelargerissueisreplacingorenhancingEDIwithanefficient,modern,structureddatadocumentstandardthatbusinesscanusetoexchangeinformation.Aswewillsee,XMListhatstandard,anditiswhatearlyadoptingbusinessesaretacklingasanintegrationmethod,evenaswespeak.SGMLTheStandardGeneralizedMarkupLanguage（SGML）isameta-markuplanguage—youcanuseameta-markuplanguagetodesignyourownmarkuplanguage（suchasXMLorHTML）.SGMLprovidesamechanismtoaddstructuretoyourdocuments,andhasagreattrackrecordofsuccessfuldeploymentsofapplications,especiallyinthepublishingrealm.But,unfortunately,SGMLhasneverbecomemainstream,largelybecauseofitscomplexity.SGMLisquitepowerful,anditcouldeasilybeusedtorepresentbusinessdata.Itspowercomesatthecostofeaseofuse,asSGMLisabittoopowerfulforeverydaybusinessapplications.Theramp-upcurveforprogrammingwithSGMLisparticularlysteep,andthehighcostofleveragingSGMLisveryprohibitive.FewpeopleuseSGMLinitsrawform,buteveryoneusesimplementationsofSGML,suchasHTMLandXML.HTMLTheHyperTextMarkupLanguage（HTML）isthepredominantstandardforWebdocuments.HTMLisanapplicationofSGMLthatisintendedformultimediapresentationofinformationovertheInternet.HTMLisaninappropriatemarkuplanguageforelectronicdata,primarilybecauseHTMLwasdesignedaroundtheuseofGUItags,ratherthanbusinessdatacontent.HTMLisgreatfordisplayingdocumentstoendusers,butitisverypoorfordefiningotherstructureinadocument.Forexample,considerthefollowingHTMLsnippet:

JohnDoeTheDoeCorporationHere,Theandtagstelltheclient-sidebrowsertorepresenttheassociatedtextinboldanditalics,respectively.However,thestructureendsthere.Thebrowserhasnowayofstructuringthesemanticmeaningofthetextwithinthedocument.Forexample,byglancingatthiscode,there’snowaywecanautomaticallyidentifythatthestring“JohnDoe”isthenameofaperson.Norcanacomputerprogramdiscernthat“TheDoeCorporation”isthenameofacompany.Notethatthereareclunkywaysaroundthis（forexample,youcouldaddIDattributes）.Similary,HTMLisnotextensible.Ifabusinessneedstoaddnewtagstoaccommodateitsneeds,thatbusinesswillrunintoawallwithHTML.ThisisbecauseHTMLisamarkuplanguage,butisnotameta-markuplanguage.XMLTheExtensibleMarkupLanguage（XML）isauniversalstandardforstructuringcontentinelectronicdocuments.XMLisextensible,enablingbusinessestoaddnewstructuretotheirdocumentsasneeded.TheXMLstandarddoesnotsuffertheversioncontrolproblemsofothermarkuplanguagessuchasHTMLbecauseithasnopredefinedtags.Rather,withXMLyoudefineyourowntagsforyourbusinessneeds.XMLisameta-markuplanguagebecauseyoucandefineyourownmarkuplanguagewhichisself-describing.ThismakesXMLtheidealdocumentformatfortransferringbusinessdataelectronically,andithasawidevarietyofotherapplicationsaswell.

BenefitsofXMLFromabusinessperspective,XMLiscompellingbecauseitallowsbusinessestostructuredatainanelegant,ex