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WSDLReading,aBeginner'sGuide

By:ThomasBayerDate:08/24/2009

ThisarticleexplainshowtoreadaWSDLdocumentbyanalyzingtheWebServicesdescriptionofapublicsampleService.DuringthearticleatreediagramisdevelopedfromthecontentoftheWSDLdocument.ThetreeillustratesthestructureofWSDL.ThereaderwillgetanunderstandingoftheWSDLelementsandtheirrelationships.TherootelementofaWSDLdocumentisdefinitions.SowestarttheWSDLtreewithadefinitionsnodeasroot.

Seefigure1:

Figure1:DefinitionandService

ToanalyseaWSDLdocumentitisrecommendedtoreaditfromthebuttomupwards.Atthebottomofthe

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BLZService'sWSDLwefindachildelementofdefinitionsnamedservice.

Listing1:ServiceElementThenameoftheserviceisBLZService.Aservicecanhavemultipleportsmarkedinfigure2witha*character.Eachportdescribesawaytoaccesstheservice.InourBLZServiceexampletherearethreeports.OneforSOAP1.1,oneforSOAP1.2andonefortheHTTPbinding.

Figure2:PortsofaService

Let'shavealookatthefirstportinlisting2.

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Listing2:PortdescribingaSOAP1.1EndpointIt'schildelementaddresshasadifferentXMLprefixthantheotherelements.TheprefixsoapisboundtotheSOAP1.1bindinginthisdocument.InsteadoftheSOAPbindingotherbindingsforJMSorafiletransportcanbeused.Theaddresselementhasoneattributenamedlocationpointingtoanendpointaddressoftheservice.

Figure3:EndpointAddress

Tomoveon,wehavetolookatthebindingattributeoftheport.Thevalue"tns:BLZServiceSOAP11Binding"pointstoabindingfurtherupinthedocument.Eachportispointingtoadifferentbindinginthisexample.AsaconsequencetheBLZServiceWSDLhasthreebindings.

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Figure4:APortreferencesaBinding

Abindingprovidesdetailsaboutaspecifictransport.Thebindinginfigure5hastwodifferenttypesofchildren.

Figure5:SOAPBinding

Firstwehavealookatthesoap:bindingelementinlisting3.ThevalueofthetransportattributeisanURIthatindicatesthatSOAPmessagesshouldbesendoverHTTP.Thevalue"document"ofthestyleattributegivesusaclueaboutthemessagestyletogetherwiththeuseattributeofthesoap:bodyelements.InourexamplewehaveaDocument/Literalmessagestyle.Abindingcanspecifydifferenttransportoptionsforeachmethodofaservice.

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Listing3:SOAP1.1BindingLet'shavealookatlisting4.ThereyoucanfindtransportoptionsforthegetBankoperation.Insidethewsdl:operationelementthereisasoap:operationelementatline2definingdetailsfortheSOAPprotocolanditstransport.ThesoapActionisareminiscentfromthepast.TheBasicProfileoftheWebServicesInteroperabilityOrganizationstipulatesthatthesoapActionshouldbeusedwithafixedvalueofanemptystring.

Listing4:BindingOperationBecauseWebServicessetthefocusonmessagesnotparameters,informationaboutthetransportofthesemessagescanbefoundinthewsdl:inputandwsdl:outputelement.Aservicemayspecifyoneorseveralfaultsasanalternativefortheoutput.

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Figure6:BindingOperation

Thesoap:bodyandsoap:headerelementscandescribeamessagefurther.Intheexamplethestyleisalwaysliteral.

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Figure7:soap:bodyElements

ItistimeagaintomoveupintheWSDL.Nowwefollowthevalueofthetypeattributeofthebinding.ItpointstoaportTypewiththesamenamefurtherupinthedocument.

Figure8:BindingreferencingaPortType

Nowwehavecrossedtheborderfromtheconcretedetailsaboutthetransportandlocationofaservicetoitspureabstractdescriptionofitsinterface.PortTypeisinWSDL1.1similartotheinterfaceoftheWebService.InWSDL2.0thetermportTypeissubstitutedwiththeterminterface.Aninterfacecanhaveseveraloperations.Anoperationcorrespondstoafunctioninproceduralprogramming.TheWSDLoftheBLZServicehasonlyoneportType.AllofthethreebindingsrefertotheoneportTypenamedBLZServicePortType.

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Figure9:OperationsofaportType

InsideaportTypewefindoperationelementsasinthebinding.Butthistimetheinputandoutputdescribethestructureofthemessagesnottransportspecificoptions.

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Figure10:InputandOutputofanOperation

ThemessageattributeoftheinputrefersagainupintheWSDLdocument.Itreferstoamessagenamedtns:getBank.Furtherupinthedocumentwefindacorrespondingmessagewiththisname.

Listing5:TheInterfaceDescriptionoftheService

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Figure11:Message

ThemessagegetBankhasonepartelementaschild.AWSDLspecialistwillrecognizethevalueoftheattributename,"parameters"indicatesthewrappersubstyleofthedocument/literalstyle.

Listing6:getBankMessageTheattributeelementatline2pointsagainfurtherup.Itreferstoanelementnamedtns:getBank.WewillfindthiselementinaXMLSchema.

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Figure12:AMessageanditsParts

Thenextchildofthedefinitionselementistypes.

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Figure13:TheTypesSection

ThetypeselementcanhavemultipleXMLschemasaschildren.

Figure14:SchemasusedinaWSDL

Listing7showsthetypeselementandanembeddedschema.

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Listing7:EmbeddedXMLSchemaInaschemawecanfindthedefinitionof:

complexTypessimpleTypes

andthedeclerationof:elements

TheXMLSchemainsideBLZServiceisatypicalschemausedforWebServicesthathasonlycomplexTypesandelementsastoplevelschemacomponents.Indocument/literalstyleallthepartspointtoelements.

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Figure15:APartcanreferenceanElement

Listing8showsthedeclarationofthegetBankelement.

Listing8:DeclarationoftheElementgetBankThetypeofthiselementisacomplexTypenamedgetBankTypedefindedsomewhereelseintheschema.

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Figure16:AnElementreferencesitsType

ThegetBankTypehasasequenceasmodulgroupcontainingoneelementnamedblzofthebuildinschematypestring.

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Figure17:AComplexTypewithaSequenceasContent

Listing9showsthedefinitionofthegetBankType.

Listing9:TheComplexTypegetBankTypeAsequencecanconsistofseveralelementsthatdescribetheorderofelementsinaSOAPmessage.

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Figure18:TheentireStructureofaWSDLDocument

FinallywearethroughtheentireWSDLdescriptionofthesampleservice.AllWSDLdocumentshavethesamestructureastheBLZService.TounderstandaWSDLstartreadingatthebottomandworkyourwayupbyfollowingtherightattributesasshowninthisarticle.IhopethisarticlewashelpfultolearnhowtoreadaWSDLdocument.

ThomasBayerbayer@predic8.com

ReferencesWSDL1.1SpecificationWSDL2.0Specification

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