外文原文CHAPTER2CREATINGXMLNOWTHATYOUHAVEAGREATERUNDERSTANDINGOFXML,HOWITCANBEUSED,ANDSOMEOFTHEJAVAAPISAVAILABLE,ITSTIMETOTURNCONCEPTSINTOPRACTICEALTHOUGHTHISBOOKISNOTBYANYMEANSADEFINITIVEGUIDETOXMLSYNTAX,OREVENANXMLREFERENCE,ITWOULDBEIMPOSSIBLETODISCUSSHOWTOPARSEANDMANIPULATEXMLDOCUMENTSWITHOUTFIRSTBEINGABLETOCREATETHOSEDOCUMENTSINADDITION,THEJAVAAPISFORHANDLINGXMLALLASSUMEAFAIRAMOUNTOFFAMILIARITYWITHXMLSYNTAXANDSTRUCTURE,ASWELLASWITHTHEDESIGNPATTERNSTHATGOINTOCREATINGANXMLDOCUMENT,CONSTRAININGIT,ANDTRANSFORMINGITTHEREFOREWELOOKATEACHOFTHESETASKSBEFOREDISCUSSINGTHECORRESPONDINGJAVAAPISTOBEGIN,WEWILLTAKEACLOSERLOOKATXMLSYNTAXINTHISCHAPTERSTARTINGWITHTHEVERYBASICXMLCONSTRUCTS,WEWILLDISCUSSWHATAWELLFORMEDXMLDOCUMENTISANDHOWTOCREATEONETHEVARIOUSXMLRULESANDSYNTACTICAL“GOTCHAS“WILLBECOVEREDTOHELPYOUBUILDXMLDOCUMENTSTHATARENOTONLYLEGAL,BUTCANBEUSEDINREALISTICAPPLICATIONSALLTHISWORKWILLSETTHESTAGEFORWRITINGOURFIRSTJAVAPROGRAMINTHENEXTCHAPTERTOUNDERSTANDHOWPARSINGXMLWORKS,ANDHOWJAVAPROVIDESCALLBACKSINTOTHEPARSINGPROCESSIFYOUHAVEEVERREADACHAPTEROREVENABOOKONAPROGRAMMINGLANGUAGESSYNTAX,YOUPROBABLYREALIZEITISUSUALLYPRETTYDRYREADINGTOTRYANDAVOIDTHIS,WEWILLLOOKATSYNTAXINABITOFADIFFERENTLIGHTTHANYOUMAYBEUSEDTORATHERTHANSTARTINGWITHASIMPLEONEORTWOLINEXMLFILEANDADDINGTOIT,WHICHTYPICALLYMAKESFORALENGTHY,USELESSFILEATTHEENDOFTHEEXERCISE,WEWILLLOOKATACOMPLETE,USABLE,RELATIVELYCOMPLEXXMLFILETHEFILEWEWILLUSEISAPORTIONOFTHEACTUALXMLDOCUMENTTHATREPRESENTSTHETABLEOFCONTENTSPAGEFORTHISBOOKWEWILLWALKTHROUGHTHISDOCUMENTLINEBYLINE,EXAMININGTHEDIFFERENTCONSTRUCTSWHATALOTOFSYNTACTICALDISCUSSIONSIGNOREISTHATINTHEREALWORLD,YOUALMOSTNEVERGETTOSEETHESIMPLEFILESTHATARESOOFTENUSEDASEXAMPLESINSTEAD,YOUSEECOMPLEXFILESTHATDONTMAKEANYSENSETOYOU,EVENAFTERREADINGABOOKYOUSHOULDGETUSEDTOSEEINGANXMLFILEWITHALLITSCONSTRUCTS,ANDBEGINTOLEARNITSSTRUCTURETHROUGHPRACTICALEXAMPLESHOPEFULLYTHISMAKESTHEDISCUSSIONATLEASTALITTLEMOREAPPLICABLEFORYOU,IFNOTSOMEWHATLESSDRYBEFOREWEBEGIN,ONEFINALOBSERVATIONTHISCHAPTERDOESNTTRYTOBEAREFERENCEINOTHERWORDS,ITDOESNTHAVEEACHTERMWITHADEFINITION,ANDITDOESNTHAVEANUTSHELLTYPEENTRYSYSTEMINSTEAD,ITISAPROGRESSIVECHAPTERDEFINITIONSAREGIVENINCONTEXTOFTHEEXAMPLESANDWHATHASALREADYBEENSAIDABOUTOTHERCONSTRUCTS,RATHERTHANEACHDEFINITIONSTANDINGALONEYOUSHOULDHAVEAGOODXMLREFERENCENEARBYFORTHERESTOFTHISBOOK,ASWEWILLNOTEXPLAINCONSTRUCTSWEGOOVERINTHISCHAPTERAGAININTHELATTERPARTOFTHEBOOK,SOWECANGETTOMOREADVANCEDTOPICSYOUMIGHTWANTTOPICKUPTHEXMLPOCKETREFERENCEBYROBERTECKSTEINOREILLY22THECONTENTWITHOURHEADERWORKEDOUT,WENOWCANMOVEONTOTHEACTUALDATACONTENTINOURXMLDOCUMENTTHISCONSISTSOFALLTHEELEMENTS,ATTRIBUTES,ANDTEXTUALDATAWITHINTHESECONSTRUCTS221THEROOTELEMENTTHEROOTELEMENTISTHEHIGHESTLEVELELEMENTINTHEXMLDOCUMENT,ANDMUSTBETHEFIRSTOPENINGTAGANDTHELASTCLOSINGTAGWITHINTHEDOCUMENTITPROVIDESAREFERENCEPOINTTHATENABLESANXMLPARSERORXMLAWAREAPPLICATIONTORECOGNIZEABEGINNINGANDENDTOANXMLDOCUMENTINOUREXAMPLE,THEROOTELEMENTISTHISTAGANDITSMATCHINGCLOSINGTAGSURROUNDALLOTHERDATACONTENTWITHINTHEXMLDOCUMENTXMLSPECIFIESTHATTHEREMAYONLYBEONEROOTELEMENTINADOCUMENTINOTHERWORDS,THEROOTELEMENTMUSTENCLOSEALLOTHERELEMENTSWITHINTHEDOCUMENTASIDEFROMTHISREQUIREMENT,AROOTELEMENTDOESNOTDIFFERFROMANYOTHERXMLELEMENTITSIMPORTANTTOUNDERSTANDTHIS,BECAUSEXMLDOCUMENTSCANREFERENCEANDINCLUDEOTHERXMLDOCUMENTSINTHESECASES,THEROOTELEMENTOFTHEREFERENCEDDOCUMENTBECOMESANENCLOSEDELEMENTINTHEREFERRINGDOCUMENT,ANDMUSTBEHANDLEDNORMALLYBYANXMLPARSERDEFININGROOTELEMENTSASSTANDARDXMLELEMENTSWITHOUTSPECIALPROPERTIESORBEHAVIORALLOWSDOCUMENTINCLUSIONTOWORKSEAMLESSLY222IDENTIFYINGXMLWITHNAMESPACESALTHOUGHWEWILLNOTDELVEDEEPLYINTOXMLNAMESPACESHERE,YOUSHOULDNOTETHEUSEOFANAMESPACEINTHEROOTELEMENTYOUPROBABLYOBSERVEDTHATALLOFTHEXMLELEMENTSNAMESAREPREFIXEDWITHJAVAXMLINOURXMLEXAMPLE,ITMAYBENECESSARYLATERTOINCLUDEPORTIONSOFOTHEROREILLYBOOKSBECAUSEEACHOFTHESEBOOKSMAYALSOHAVE,ORTAGS,THEDOCUMENTMUSTBEDESIGNEDANDCONSTRUCTEDINAWAYTOAVOIDNAMESPACECOLLISIONPROBLEMSWITHOTHERDOCUMENTSTHEXMLNAMESPACESSPECIFICATIONNICELYSOLVESTHISPROBLEMBECAUSEOURXMLDOCUMENTREPRESENTSASPECIFICBOOK,ANDNOOTHERXMLDOCUMENTSHOULDREPRESENTTHESAMEBOOK,USINGAPREFIXLIKEJAVAXMLCANASSOCIATETHEELEMENTTOANAMESPACETHENAMESPACESPECIFICATIONREQUIRESTHATAUNIQUEURIBEASSOCIATEDWITHTHEPREFIXTODISTINGUISHTHEELEMENTSINTHENAMESPACEFROMELEMENTSINOTHERNAMESPACESAURLISRECOMMENDED,WHICHISWHATISSUPPLIEDHEREHTTP/WWWOREILLYCOM/CATALOG/JAVAXML,THEWEBSITEFORTHEBOOKONCETHENAMESPACEISDEFINEDLIKETHIS,ITCANTHENBEREFERENCEDBYANYOTHERELEMENTWITHINTHEXMLDOCUMENTINOURCASE,WEUSEITFORALLOFTHEELEMENTSBECAUSETHEYAREALLPARTOFTHEBOOKSNAMESPACETHEPROPERWAYTOASSOCIATEANELEMENTWITHANAMESPACEISTOPREFIXTHENAMEOFTHEELEMENTWITHTHENAMESPACEPREFIXANDACOLONINTRODUCTIONWHATISITHOWDOIUSEITWHYSHOULDIUSEITWHATSNEXTEACHOFTHESEELEMENTSISTREATEDBYTHEXMLPARSERASPARTOFTHEHTTP/WWWOREILLYCOM/CATALOG/JAVAXML/NAMESPACE,ANDWILLNOTRESULTINCOLLISIONSWITHANYOTHERELEMENTSNAMEDCHAPTER,HEADING,ORTOPICWITHINOTHERNAMESPACESMULTIPLENAMESPACEDECLARATIONSCANBEINCLUDEDINTHESAMEDOCUMENT,ALLWITHINTHESAMEELEMENTALTHOUGHTHISISALEGALDECLARATION,BEVERYCAREFULWHENUSINGMULTIPLENAMESPACESWITHINONEDOCUMENTOFTEN,THEBENEFITSOFUSINGNAMESPACESCANBEOUTWEIGHEDBYTHEADDITIONALCLUTTERANDTEXTUALDATATHEYADDTOTHEDOCUMENTGENERALLY,ASINGLENAMESPACEFORASINGLEDOCUMENTPROVIDESACLEAR,CLEANXMLDOCUMENTWHILESTILLAVOIDINGNAMESPACECOLLISIONSTHEONLYNOTABLEEXCEPTIONISWHENANOTHERXMLSPECIFICATIONSUCHASXMLSCHEMAISUSEDANDTHATNAMESPACEMUSTBEREFERENCEDAFINALINTERESTINGANDSOMEWHATCONFUSINGPOINTXMLSCHEMA,WHICHWEWILLTALKABOUTMOREINCHAPTER4,REQUIRESTHESCHEMAOFANXMLDOCUMENTTOBESPECIFIEDINAMANNERTHATLOOKSVERYSIMILARTOASETOFNAMESPACEDECLARATIONSSEEEXAMPLE22EXAMPLE22XMLDOCUMENTUSINGXMLSCHEMABRETTMCLAUGHLINBRETTMCLAUGHLINEARTHLINKNETEDDIEBALUCCIEDDIEBFREEWORLDNETSEVERALTHINGSHAPPENHERE,ANDITISIMPORTANTTOUNDERSTANDEACHFIRST,THEXMLSCHEMAINSTANCENAMESPACEISDEFINEDANDASSOCIATEDWITHAURLTHISNAMESPACE,ABBREVIATEDXSI,ISUSEDFORSPECIFYINGINFORMATIONINXMLDOCUMENTSABOUTASCHEMA,EXACTLYASWEAREDOINGHERETHUS,OURFIRSTLINEMAKESTHEELEMENTSINTHEXMLSCHEMAINSTANCEAVAILABLETOOURDOCUMENTFORUSETHENEXTLINEDEFINESTHENAMESPACEFORTHEXMLDOCUMENTITSELFBECAUSETHEDOCUMENTDOESNOTUSEANEXPLICITNAMESPACE,LIKEJAVAXMLINEARLIEREXAMPLES,THEDEFAULTNAMESPACEISDECLAREDTHEXMLNAMESPACESSPECIFICATIONDICTATESTHATEVERYELEMENTINANXMLDOCUMENTISINANAMESPACETHEDEFAULTNAMESPACEISTHENAMESPACETHATANELEMENTISASSOCIATEDWITHIFNOOTHERNAMESPACEISSPECIFIEDTHISMEANSTHATALLELEMENTSWITHOUTANEXPLICITNAMESPACEANDASSOCIATEDPREFIXALLOFTHEM,INTHISEXAMPLEWILLBEASSOCIATEDWITHTHISDEFAULTNAMESPACEWITHBOTHTHEDOCUMENTANDXMLSCHEMAINSTANCENAMESPACESDEFINEDLIKETHIS,WECANTHENACTUALLYDOWHATWEWANT,WHICHISTOASSOCIATEASCHEMAWITHTHISDOCUMENTTHESCHEMALOCATIONATTRIBUTE,WHICHBELONGSTOTHEXMLSCHEMAINSTANCENAMESPACE,ISUSEDTOACCOMPLISHTHISWEPREFACETHISATTRIBUTEWITHITSNAMESPACEXSI,WHICHWEJUSTDEFINEDTHEARGUMENTTOTHISATTRIBUTEISACTUALLYTWOURISTHEFIRSTSPECIFYINGTHENAMESPACEBEINGASSOCIATEDWITHASCHEMA,ANDTHESECONDTHEURIOFTHESCHEMATOREFERTOINOUREXAMPLE,THISRESULTSINTHEFIRSTURIBEINGTHEDEFAULTNAMESPACEWEJUSTDECLARED,ANDTHESECONDAFILEONTHELOCALFILESYSTEMCALLEDMYSCHEMAXSDLIKEANYOTHERXMLATTRIBUTE,THISENTIREPAIRISENCLOSEDINASINGLESETOFQUOTATIONMARKSANDASSIMPLEASTHAT,YOUHAVEREFERENCEDASCHEMAINYOURXMLDOCUMENTSERIOUSLY,THISISNOTSIMPLE,ANDISTODATEONEOFTHEMOSTMISUNDERSTOODPORTIONSOFUSINGNAMESPACESANDXMLSCHEMAWEWILLLOOKMOREATTHEMECHANICSUSEDHEREASWECONTINUEFORNOW,TRYTOUNDERSTANDHOWNAMESPACESALLOWELEMENTSFROMVARIOUSGROUPINGSTOBEUSED,YETREMAINIDENTIFIEDASAPARTOFTHEIRSPECIFICGROUPING223XMLDATAELEMENTSSOFARWEHAVEGLOSSEDOVERDEFININGWHATANACTUALELEMENTISNOWWEWILLTAKEANINDEPTHLOOKATELEMENTS,WHICHAREREPRESENTEDBYARBITRARYNAMESANDMUSTBEENCLOSEDINANGLEBRACKETSTHEREARESEVERALDIFFERENTVARIATIONSOFELEMENTSINTHESAMPLEDOCUMENT,ASSHOWNHEREWEBPUBLISHINGFRAMEWORKSTHEFIRSTRULEINCREATINGELEMENTSISTHATTHEIRNAMESMUSTSTARTWITHALETTERORUNDERSCORE,ANDTHENMAYCONTAINANYNUMBEROFLETTERS,NUMBERS,UNDERSCORES,HYPHENS,ORPERIODSTHEYMAYNOTCONTAINEMBEDDEDSPACESTHEFOLLOWINGISNOTWELLFORMEDXMLXMLELEMENTNAMESAREALSOCASESENSITIVEGENERALLY,USINGTHESAMERULESTHATGOVERNJAVAVARIABLENAMINGWILLRESULTINSOUNDXMLELEMENTNAMINGUSINGANELEMENTNAMEDTOREPRESENTTELECOMMUNICATIONSBUSINESSOBJECTNOTAGOODIDEABECAUSEITISCRYPTIC,WHILEANOVERLYVERBOSETAGNAMELIKEJUSTCLUTTERSUPADOCUMENTKEEPINMINDTHATYOURXMLDOCUMENTSWILLPROBABLYBESEENBYOTHERDEVELOPERSANDCONTENTAUTHORS,SOSELFDOCUMENTATIONTHROUGHGOODNAMINGISESSENTIALEVERYOPENEDELEMENTMUSTINTURNBECLOSEDTHEREARENOEXCEPTIONSTOTHISRULEASTHEREAREINMANYOTHERMARKUPLANGUAGES,LIKEHTMLANENDINGELEMENTTAGCONSISTSOFTHEFORWARDSLASHANDTHENTHEELEMENTNAMEBETWEENANOPENINGANDCLOSINGTAG,THERECANBEANYNUMBEROFADDITIONALELEMENTSORTEXTUALDATAHOWEVER,YOUCANNOTMIXTHEORDEROFNESTEDTAGSTHEFIRSTOPENEDELEMENTMUSTALWAYSBETHELASTCLOSEDELEMENTIFANYOFTHERULESFORXMLSYNTAXARENOTFOLLOWEDINANXMLDOCUMENT,THEDOCUMENTISNOTWELLFORMEDAWELLFORMEDDOCUMENTISONEINWHICHALLXMLSYNTAXRULESAREFOLLOWED,ANDALLELEMENTSANDATTRIBUTESARECORRECTLYPOSITIONEDHOWEVER,AWELLFORMEDDOCUMENTISNOTNECESSARILYVALID,WHICHMEANSTHATITFOLLOWSTHECONSTRAINTSSETUPONADOCUMENTBYITSDTDORSCHEMATHEREISASIGNIFICANTDIFFERENCEBETWEENAWELLFORMEDDOCUMENTANDAVALIDONETHERULESWEDISCUSSINTHISCHAPTERENSURETHATYOURDOCUMENTISWELLFORMED,WHILETHERULESDISCUSSEDINCHAPTER4ALLOWYOURDOCUMENTTOBEVALIDASANEXAMPLEOFADOCUMENTTHATISNOTWELLFORMED,CONSIDERTHISXMLFRAGMENTTHEORDEROFNESTINGOFTAGSISINCORRECT,ASTHEOPENEDISNOTFOLLOWEDBYACLOSINGWITHINTHESURROUNDINGTAG1ELEMENTHOWEVER,IFTHESESYNTAXERRORSARECORRECTED,THEREISNOGUARANTEETHATTHEDOCUMENTWILLBEVALIDTHISISANIMPORTANTDIFFERENCETOUNDERSTAND,ANDWEWILLREVISITTHESUBJECTINCHAPTER4WHILETHISEXAMPLEOFADOCUMENTTHATISNOTWELLFORMEDMAYSEEMSILLYANDTRIVIAL,REMEMBERTHATTHISWOULDBEACCEPTABLEHTML,ANDCOMMONLYOCCURSINLARGETABLESWITHINANHTMLDOCUMENTINOTHERWORDS,HTMLANDMANYOTHERMARKUPLANGUAGESDONOTREQUIREWELLFORMEDXMLDOCUMENTSXMLSSTRICTADHERENCETOORDERINGANDNESTINGRULESALLOWSDATATOBEPARSEDANDHANDLEDMUCHMOREQUICKLYTHANWHENUSINGMARKUPLANGUAGESWITHOUTTHESECONSTRAINTSTHELASTRULEWELOOKATISTHESLIGHTLYODDCASEOFEMPTYELEMENTSWEALREADYSAIDTHATXMLTAGSMUSTALWAYSBEPAIREDANOPENINGTAGANDACLOSINGTAGCONSTITUTEACOMPLETEXMLELEMENTTHEREARECASESWHEREANELEMENTISUSEDPURELYBYITSELF,LIKEAFLAGSTATINGACHAPTERISINCOMPLETE,ORWHEREANELEMENTHASATTRIBUTESBUTNOTEXTUALDATA,LIKEANIMAGEDECLARATIONINHTMLTHESEWOULDHAVETOBEREPRESENTEDASTHISISOBVIOUSLYABITSILLY,ANDALSOADDSMORECLUTTERTOWHATCANOFTENBEVERYLARGEXMLDOCUMENTSTHEXMLSPECIFICATIONPROVIDESAMEANSTOSIGNIFYBOTHANOPENINGANDCLOSINGELEMENTTAGWITHINONEELEMENTTHISNICELYSOLVESTHEPROBLEMOFUNNECESSARYCLUTTER,ANDSTILLFOLLOWSTHERULETHATEVERYXMLELEMENTMUSTHAVEAMATCHINGENDTAGITSIMPLYCONSOLIDATESBOTHSTARTANDENDTAGINTOASINGLETAG224ELEMENTATTRIBUTESINADDITIONTOTEXTCONTAINEDWITHINANELEMENTSTAGS,ANELEMENTCANALSOHAVEATTRIBUTESATTRIBUTESAREINCLUDEDWITHTHEIRRESPECTIVEVALUESWITHINTHEELEMENTSOPENINGDECLARATIONWHICHCANALSOBEITSCLOSINGDECLARATIONFOREXAMPLE,INTHEJAVAXMLCHAPTERTAG,THEFOCUSOFTHECHAPTERWASPARTWHATOFWASNOTEDINANATTRIBUTEINTHISEXAMPLE,FOCUSISTHEATTRIBUTENAMETHEVALUEISTHEFOCUSOFTHECHAPTER,XMLANDJAVA,RESPECTIVELYATTRIBUTENAMESMUSTFOLLOWTHESAMERULESASXMLELEMENTNAMES,ANDATTRIBUTEVALUESMUSTBEWITHINQUOTATIONMARKSALTHOUGHBOTHSINGLEANDDOUBLEQUOTESAREALLOWED,USINGDOUBLEQUOTESISAWIDELYUSEDSTANDARDANDRESULTSINXMLDOCUMENTSTHATMODELJAVAPROGRAMMINGPRACTICESADDITIONALLY,SINGLEANDDOUBLEQUOTATIONMARKSMAYBEUSEDINATTRIBUTEVALUESSURROUNDINGTHEVALUEINDOUBLEQUOTESALLOWSSINGLEQUOTESTOBEUSEDASPARTOFTHEVALUE,ANDSURROUNDINGTHEVALUEINSINGLEQUOTESALLOWSDOUBLEQUOTESTOBEUSEDASPARTOFTHEVALUETHISISGOODPRACTICE,THOUGH,ASXMLPARSERSANDPROCESSORSOFTENUNIFORMLYCONVERTTHEQUOTESROUNDANATTRIBUTESVALUETOALLDOUBLEORALLSINGLEQUOTES,POSSIBLYINTRODUCINGUNEXPECTEDRESULTSINADDITIONTOHOWTOUSEATTRIBUTES,THEREISANISSUEOFWHENTOUSEATTRIBUTESBECAUSEXMLALLOWSSUCHVARIETYOFDATAFORMATTING,ITISRARETHATANATTRIBUTECANNOTBEREPRESENTEDBYANELEMENT,ORTHATELEMENTCOULDNOTEASILYBECONVERTEDTOANATTRIBUTEALTHOUGHTHEREISNOSPECIFICATIONORWIDELYACCEPTSTANDARDFORDETERMININGWHENTOUSEANATTRIBUTEANDWHENTOUSEANELEMENT,HEREISAGOODRULEOFTHUMBUSEELEMENTSFORPRESENTABLEDATAANDATTRIBUTESFORSYSTEMDATAIFHAVEAPIECEOFDATATHATISGOINGTOBEPRESENTEDTOACLIENT,ORANAPPLICATION,ORUSEDASPARTOFFORMULA,THEDATAMOSTLIKELYBELONGSINANELEMENTITCANTHENBETREATEDPRIMARILYASAPPLICATIONDATAANDISEASILYSEARCHABLEANDUSABLEEXAMPLESARETHETITLESOFABOOKSCHAPTERS,THEPRICEOFFURNITURE,ORTHEURLOFACOMPANYSWEBSITEHOWEVER,IFTHEDATAISUSEDASAGROUPING,LETANAPPLICATIONKNOWHOWTOHANDLEAPORTIONOFDATA,ORISNEVERDIRECTLYVISIBLETOACLIENTORXMLAWAREAPPLICATION,ITMOSTLIKELYBELONGSASANATTRIBUTEEXAMPLESOFGOODCANDIDATESFORATTRIBUTEARETHESECTIONOFACHAPTERWHILETHESECTIONITEMITSELFMIGHTBEANELEMENTANDHAVEITSOWNTITLE,THEGROUPINGOFCHAPTERSWITHINASECTIONISEASILYREPRESENTEDBYASECTIONATTRIBUTEWITHINTHEJAVAXMLCHAPTERELEMENTTHISATTRIBUTEWOULDALLOWEASYGROUPINGANDINDEXINGOFCHAPTERS,BUTWOULDNEVERBEDIRECTLYDISPLAYEDTOTHEUSERANOTHERGOODEXAMPLEOFAPIECEOFDATATHATCOULDBEREPRESENTEDINXMLASANATTRIBUTEISIFAPARTICULARTABLEORCHAIRISONLAYAWAYTHISINSTRUCTIONCOULDLETANXMLAPPLICATIONUSEDTOGENERATEABROCHUREORFLYERKNOWNOTTOINCLUDEITEMSONLAYAWAYINCURRENTSTOCKAGAIN,THEAPPLICATIONCLIENTWOULDNEVERDIRECTLYSEETHISINFORMATION,BUTTHEDATAWOULDBEUSEDINPROCESSINGANDHANDLINGTHEXMLDOCUMENTIFAFTERALLOFTHISANALYSISYOUARESTILLUNSURE,YOUCANALWAYSPLAYITSAFEANDUSEANELEMENTYOUMAYHAVEALREADYCOMEUPWITHALTERNATEWAYSTOREPRESENTTHESEVARIOUSEXAMPLES,USINGDIFFERENTAPPROACHESFOREXAMPLE,RATHERTHANUSINGASECTIONATTRIBUTE,ITMIGHTMAKESENSETONESTJAVAXMLCHAPTERELEMENTSWITHINAJAVAXMLSECTIONELEMENTPERHAPSANEMPTYTAG,MIGHTBEMOREUSEFULTOMARKFURNITURETHATISONLAYAWAYINXML,THEREISRARELYONLYONEWAYTOPERFORMDATAREPRESENTATION,ANDOFTENSEVERALGOODWAYSTOACCOMPLISHTHESAMETASKMOSTOFTENTHEAPPLICATIONANDUSEOFTHEDATADICTATESWHATMAKESTHEMOSTSENSERATHERTHANTRYTOTELLYOUHOWTOWRITEXML,WHICHWOULDBEDIFFICULT,WEWILLUSEXML,ANDINTHATUSEYOUWILLHOPEFULLYGAININSIGHTINTOHOWDIFFERENTDATAFORMATSCANBEHANDLEDANDUSEDTHISWILLTHENGIVEYOUTHEKNOWLEDGETOMAKEYOUROWNDECISIONSABOUTFORMATTINGXMLDOCUMENTS225REFERRINGTOXML“CONSTANTS“ONEITEMWEHAVENOTDISCUSSEDISESCAPINGCHARACTERS,ORREFERRINGTOOTHERCONSTANTTYPEDATAVALUESFOREXAMPLE,ACOMMONWAYTOREPRESENTAPATHTOANINSTALLATIONDIRECTORYISORINBOTHTHESECASES,THEUSERWOULDREPLACETHETEXTWITHTHEAPPROPRIATECHOICEOFINSTALLATIONDIRECTORYINOUREXAMPLE,THECHAPTERTHATDISCUSSESWEBAPPLICATIONSNEEDSTOGIVESOMEDETAILSONINSTALLINGANDUSINGAPACHECOCOON,ANDMIGHTNEEDTOREPRESENTTHISDATAWITHINANELEMENTINSTALLINGCOCOONLOCATETHECOCOONPROPERTIESFILEINTHE/BINDIRECTORYTHEPROBLEMWITHTHISISTHATXMLPARSERSWILLATTEMPTTOHANDLETHISDATAASANXMLTAG,ANDTHENGENERATEANERRORBECAUSETHEREISNOCLOSINGTAGTHISISACOMMONPROBLEM,ASANYUSEOFANGLEBRACKETSRESULTSINTHISBEHAVIORENTITYREFERENCESPROVIDEAWAYTOOVERCOMETHESEPROBLEMSANENTITYREFERENCEISASPECIALDATATYPEINXMLTHATISUSEDTOREFERTOANOTHERPIECEOFDATATHEENTITYREFERENCECONSISTSOFAUNIQUENAME,PRECEDEDBYANAMPERSANDANDFOLLOWEDBYASEMICOLONWHENANXMLPARSERSEESANENTITYREFERENCE,THESUBSTITUTIONVALUESPECIFIEDISINSERTEDANDNOPROCESSINGOFTHATVALUEOCCURSXMLDEFINESFIVEENTITIESTOADDRESSTHEPROBLEMDISCUSSEDINTHEEXAMPLEFORTHELESSTHANBRACKET,FORTHEGREATERTHANBRACKET,FORTHEAMPERSANDSIGNITSELF,FORADOUBLEQUOTATIONMAR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