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Introduction toWSDL

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WhatYouShouldAlreadyKnow

Beforeyoucontinueyoushouldhaveabasic

understandingofthefollowing: XML

XMLNamespaces XMLSchema

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WhatisWSDL?

WSDLstandsforWebServicesDescription

Language WSDLiswritteninXML

WSDLisanXMLdocument WSDLisusedtodescribeWebservices

WSDLisalsousedtolocateWebservices WSDLisaW3Crecommendation

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WSDLDescribesWebServices

WSDLstandsforWebServicesDescription

Language. WSDLisadocumentwritteninXML.The

document

describes

a

Web

service.

It

specifies

thelocationoftheserviceandtheoperations

(ormethods)theserviceexposes.

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TheWSDLDocumentStructure

Element Defines

Thedatatypesusedbythewebservice

Themessagesusedbythewebservice

Theoperationsperformedbythewebservice

Thecommunicationprotocolsusedbythewebservice

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ThemainstructureofaWSDL

documentlookslikethis:

definitionoftypes........

definitionofamessage....

definitionofaport.......

definitionofabinding....

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WSDLPorts

The

elementisthemostimportant

WSDL

element. Itdescribesawebservice,theoperationsthatcanbeperformed,andthemessagesthatare

involved. Theelementcanbecomparedtoafunctionlibrary(oramodule,oraclass)ina

traditionalprogramminglanguage.

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WSDLMessages

The

elementdefinesthedata

elementsofanoperation. Eachmessagecanconsistofoneormore

parts.

The

parts

can

be

compared

to

the

parametersofafunctioncallinatraditional

programminglanguage.

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WSDLTypes

The

elementdefinesthedatatypes

thatareusedbythewebservice. Formaximumplatformneutrality,WSDLuses

XML

Schema

syntax

to

define

data

types.

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WSDLExample

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SOAP

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WhatisSOAP?

SOAPstandsforSimpleObjectAccessProtocol

SOAPisacommunicationprotocol

SOAPisforcommunicationbetweenapplications

SOAPisaformatforsendingmessages

SOAPcommunicatesviaInternet

SOAPisplatformindependent SOAPislanguageindependent

SOAPisbasedonXML

SOAPissimpleandextensible SOAPallowsyoutogetaroundfirewalls

SOAPisaW3Crecommendation

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WhySOAP?

ItisimportantforapplicationdevelopmenttoallowInternetcommunicationbetweenprograms.

Today'sapplicationscommunicateusingRemoteProcedureCalls(RPC)betweenobjectslikeDCOMandCORBA,butHTTPwasnotdesignedforthis.RPCrepresentsacompatibilityandsecurityproblem;firewallsandproxy

serverswillnormallyblockthiskindoftraffic. AbetterwaytocommunicatebetweenapplicationsisoverHTTP,becauseHTTPissupportedbyallInternetbrowsers

and

servers.

SOAP

was

created

to

accomplish

this. SOAPprovidesawaytocommunicatebetweenapplicationsrunningondifferentoperatingsystems,withdifferenttechnologiesandprogramminglanguages

SOAP B ildi Bl k

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SOAPBuildingBlocks

ASOAPmessageisanordinaryXMLdocumentcontainingthefollowingelements:

AnEnvelopeelementthatidentifiestheXMLdocumentasaSOAPmessage

A

Header

element

that

contains

header

information

ABodyelementthatcontainscallandresponseinformation

AFaultelementcontainingerrorsandstatusinformation

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SyntaxRules

Herearesomeimportantsyntaxrules:

A

SOAP

message

MUST

be

encoded

using

XML ASOAPmessageMUSTusetheSOAPEnvelopenamespace

ASOAPmessageMUSTusetheSOAPEncodingnamespace

ASOAPmessagemustNOTcontainaDTD

reference ASOAPmessagemustNOTcontainXMLProcessingInstructions

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...

... ...

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TheSOAPEnvelopeElement

TherequiredSOAPEnvelopeelementistherootelementofaSOAPmessage.ThiselementdefinestheXML

documentasaSOAPmessage. Example

... Messageinformationgoeshere ...

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SOAP Header Element TheoptionalSOAPHeaderelementcontains

applicationspecificinformation(likeauthentication,payment,etc)abouttheSOAP

message.

IftheHeaderelementispresent,itmustbethe

firstchildelementoftheEnvelopeelement.

Note: AllimmediatechildelementsoftheHeaderelementmustbenamespacequalified.

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soap:actor="http://www.w3schools.com/appml/">

... ...

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SOAPdefinesthreeattributesinthedefault

namespace("http://www.w3.org/2001/12/soap envelope").Theseattributesare:mustUnderstand,actor,andencodingStyle.

TheattributesdefinedintheSOAPHeader

defineshowarecipientshouldprocessthe

SOAPmessage.

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ThemustUnderstand Attribute TheSOAPmustUnderstand

attributecanbeused

toindicatewhetheraheaderentryismandatoryoroptionalfortherecipienttoprocess.

IfyouaddmustUnderstand="1"toachild

elementoftheHeaderelementitindicatesthat

thereceiverprocessingtheHeadermust

recognize

the

element.

If

the

receiver

does

not

recognizetheelementitwillfailwhenprocessing

theHeader.

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TheactorAttribute

ASOAPmessagemaytravelfromasenderto

a

receiver

by

passing

different

endpoints

alongthemessagepath.

However,notallpartsofaSOAPmessage

maybeintendedfortheultimateendpoint,instead,itmaybeintendedforoneormoreoftheendpointsonthemessagepath.

TheSOAPactorattributeisusedtoaddresstheHeaderelementtoaspecificendpoint.

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TheencodingStyle Attribute TheencodingStyle

attributeisusedtodefine

thedatatypesusedinthedocument.ThisattributemayappearonanySOAPelement,

anditwillapplytothatelement'scontents

andallchildelements.

ASOAPmessagehasnodefaultencoding.

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TheSOAPFaultElement

TheoptionalSOAPFaultelementisusedto

indicateerrormessages. IfaFaultelementispresent,itmustappearas

a

child

element

of

the

Body

element.

A

Fault

elementcanonlyappearonceinaSOAP

message.

The SOAP Fault element has the

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TheSOAPFaultelementhasthe

followingsubelements:

SubElement Description

Acodeforidentifyingthefault

Ahumanreadableexplanationofthefault

Informationaboutwhocausedthefaulttohappen

Holdsapplicationspecificerrorinformationrelatedto

theBodyelement