CS4720

WebServicesandServiceOrientedArchitecture

CS4720– MobileApplicationDevelopment

CS4720

Thetraditionalsoftwaremodel• Organizationsbuilditallfromscratch

– “Wecan'ttrustanyone!Ourcompetitorswillsabotageus!”

– “Wemustowneverything!Hardwareandsoftware!”

• CompaniesthatbuildsoftwareneedcomponentsthatdoXorY…– …sotheybuyCOTScomponents– Servicecontracts,newreleases,regressiontesting…

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Thetraditionalsoftwaremodel• Howwelldoesthiswork?• SomeprojectdatafromtheDOD:

– 47%ofsoftwaredeliveredcouldnotbeused• Usuallydidn'tmeetrequirements

– 29%offundedsoftwareneverdelivered• Usuallycanceledduetocost/scheduleoverruns

– 19%ofsoftwareusefulafterextensiverework• Costs36timesmoretofixproblemsafterrelease

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Apushtodistribution• “We'rereallygoodat__________,howcanwegetour__________outforpeopletouse?”

• Theideaofdistributedcomputing– “We'regoodatX,butnotsogoodaY…”– “WhatifwegotsomeonetohelpuswithY…butinawaythatwedidn’thavetoincludeanyfancylibraries…

– …andwecouldusetheminwebapps!Andmobiledevices!Andevendesktopapps!”

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AWebService• FromW3C:“asoftwaresystemdesignedtosupportinteroperablemachine-to-machineinteractionoveranetwork.Ithasaninterfacedescribedinamachine-processableformat(specificallyWSDL).OthersystemsinteractwiththeWebserviceinamannerprescribedbyitsdescriptionusingSOAP-messages,typicallyconveyedusingHTTPwithanXMLserializationinconjunctionwithotherWeb-relatedstandards”

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AWebService?• Huh?• Abitmoresimply:Aprogram,accessibleviatheInternet,thatcandosomefunction(eitherforfreeorafee)andcanbedynamicallydiscoveredandused.

• So…Iusewebappsallthetime…arethosewebservices?

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WebServiceasRPC• Theearliestformofatrue“webservices” wasanRPC– remoteprocedurecall.

• Exactlywhatitsoundslike– thereisanexposedfunction/methodthatisaccessedviathewebwhereyoupasstheparametersandthemethodnameandyougetbackareturnvalue.

• NoticehowthisisverydifferentfromtheRESTfulmodel(verbsvs.nouns)

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WebServiceasSOA• RPCwasokay…butitturnedouttobeabitmorelanguagespecificthanwe'dlike

• Whatifwejustastructuredmessage(likeanXMLdocument)thatdescribedwhatwewanted,asopposedtoknowingtheexactfunctioncall?

• ThisisthebasisoftheService-OrientedArchitecture

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WordByWord• Whatisaservice?• "Aserviceisadiscoverableresourcethatexecutesarepeatabletask,andisdescribedbyanexternalizedservicespecification.”

• Businessalignment– businessrequirements• Specifications– self-contained,wellspecified• Reusability– generalenoughtobereused• Agreements– basedonfunction,notplatform• Hostinganddiscoverability– available• Aggregation– canbecombinedtomakebiggerservices

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WordByWord• Whatisanarchitecture?• "Aformaldescriptionofasystem,oradetailedplanofthesystematcomponentleveltoguideitsimplementation.”

• “Thestructureofcomponents,theirinterrelationships,andtheprinciplesandguidelinesgoverningtheirdesignandevolutionovertime."

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Architecture

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• Architectureis:– Ahigh-enoughlevelofabstractionthatthesystemcanbeviewedasawholeandyetstillprovidesenoughinformationtomakedecisions.

– Supportsthefunctionalityofthesystem.– Allimplementationdetailsarehidden.

• Serviceorientationisawayofintegratingabusinessasasetoflinkedservices.

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Whatareweactuallytryingtodo?

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Receive PO

Get Items from InventoryUpdate Customer Profile

Compute Subtotal

Compute Shipping Cost

Compute Export Tax

Compute International Shipping

Compute Total

[ship within US] [ship outside US]

Ship Order

Fork

Join

Branch

Merge

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SOA– TheQuickVersion• Rightnow,youprobablythinkofasoftwaresystemasbeingacollectionofclasses/objects

• Butusersdon'tthinkofsystemslikethat…theythinkofsystemsassetsoffunctionalitythathelpthemdosomething

• So…whydoweuseobjects?– Easiertomodel– Easiertoprogram– Easiertoexplaintootherprogrammers

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Orisitactuallyeasier?• Turnourideaofasystem90degrees• Functionalityobjects(proceduralabstraction)isthekeyidea,notworldobjects(dataabstraction)

• ThisisthekeyinSOA– AnSOAsystemhasthefunctionalitiesasthemainplayers,nottheobjectsthemselves

– Butmoreso,theseservicesareprovidedbymanydifferentplayers

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Butwhatlanguagedowespeak?• OneearlywaytodowebserviceswaswithSOAP

• SOAP- SimpleObjectAccessProtocol– Acommunicationprotocol– Aformatforsendingmessages– XMLbased

• NotreallymuchmorethananHTTPrequestthatfollowsXML/SOAPstandards

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SOAPModel

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SOAPModel

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SOAPRequestPOST /InStock HTTP/1.1Host: www.example.orgContent-Type: application/soap+xml; charset=utf-8Content-Length: nnn

<?xml version="1.0"?><soap:Envelopexmlns:soap="http://www.w3.org/2001/12/soap-envelope"soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Body xmlns:m="http://www.example.org/stock"><m:GetStockPrice>

<m:StockName>IBM</m:StockName></m:GetStockPrice>

</soap:Body>

</soap:Envelope>

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SOAPResponse• HTTP/1.1 200 OK

Content-Type: application/soap+xml; charset=utf-8Content-Length: nnn

<?xml version="1.0"?><soap:Envelopexmlns:soap="http://www.w3.org/2001/12/soap-envelope"soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Body xmlns:m="http://www.example.org/stock"><m:GetStockPriceResponse>

<m:Price>34.5</m:Price></m:GetStockPriceResponse>

</soap:Body>

</soap:Envelope>

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PartsofSOAP• TheEnvelope– requiredrootelementdefiningthedocumentasbeingaSOAPrequest

• TheHeader– notrequired,butcontainsauthenticationand/orpaymentinfofortherequest

• TheBody– theactualmessagebeingsent

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UsingaWebService• Ifyoutookthetimetocreateaservice,thenyouprobablywantpeopletouseit

• Inordertouseaservice,usersneedtoknowwhatinformationtheycansendtheserviceandwhatinformationisgoingtobesentback

• Whatwouldbeevenbetterisifthesoftwarecoulddoallthisautomatically…

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EnterWSDL• WSDL:WebServicesDescriptionLanguage

– AnXMLdocumentusedtogivethespecificsofaservice• Location• Methods• Allowedmessages• Potentialerrormessages

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EnterWSDL

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QuickSidestep:UDDI• UDDI:UniversalDescription,DiscoveryandIntegration

• Asolutioninsearchofaproblem• Theideaisokay:alanguageandschemaforallowingpeopletopublishtheirWSDLschemassothatotherscandiscovertheirservices

• IBM,Microsoft,andSAPannouncedtheywereclosingtheirpublicUDDInodesinJanuary2006

• Nooneusedit!

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QuickSidestep:UDDI• Wheremightitworkdecently?

– Perhapsinsideasingleorganizationforinternalcode

• Thepublicsideswereeither:– Empty– Overrunwithjunk

• WhicheveritwasUDDI,isn'treallyused• QuoteMartyHumphrey:“Itwasagoodproblemtosolve,butaterriblesolution.”

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TheOriginalIdea

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BacktoWSDL• WeDOuseWSDLthough• Itishowawebserviceisboundtoanapplication

• It'smoreXML…• But…thebestpartis…

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TheBestPartaboutWSDL• Nooneeverwritesthestuffthemselves!• It'sauto-generated!

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TheWorstPart• Thiswasreallycomplicated• Evenwithauto-generatingcode,itwastoughtobuildandmaintain

• Itmadeiteasierforwhoeverwantedtoconsumetheservice(theoretically),buteventhentherewasalotofsetup

• PeoplewerealreadystartingtoparsetheirownXMLorJSON…

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ModernRESTAPIs• MostallmodernRESTwebservicesnowoperateusingJSON– JavaScriptObjectNotation– Easytoparse– Easytocreate– MostwebappsarealreadyusingJavaScript,soitworksseamlessly

– JSONparsingisn’texpensiveforotherplatforms

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ModernRESTAPIs• Considerhttps://dev.twitter.com/rest/public• Let’sexaminetheseinthecontextofthefiveaspectsofREST

• ThepurposeofaRESTAPIwebserviceisto:– Exposefunctionalityforotherstouse– Allowthatfunctionalitytobebuiltintootherapps– Makeiteasytouseforvariousplatforms– Stillallowthedevelopertomakemoneysomewayontheservice

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CS4720

Whichbringsusbacktomobile!• Withmobile:

– WelikeREST!Itworkswellwithnetworkthatcomesandgoesandhowweusemobiledevices!

– WelikeMVC!Itmakessenseinhowwebuildourapps!

– Welikewebservices!Itallowsustoutilizepowerfulfeaturesdevelopedbyotherstomakeourownappsevenbetter!

– Now… howdowedoit???

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