SOFTWARE ARCHITECTURAL STYLES

Transcription

1 SOFTWARE ARCHITECTURAL STYLES Sean Boyd, Mark D Adamo, Christopher Horne, Nolan Kelly, David Ryan, Nairn Tsang SENG W2013 Paper Project (Group 4)

2 Table&of&Contents& IntroductiontoSoftwareArchitecturalStyles...3 MessageBusArchitecture...3 Pros...3 Cons...3 Client/ServerArchitecture...4 Pros([13])...4 Cons([13])...4 Example MicrosoftSQLServer...5 Pros...5 Cons...5 Example Cocoa...6 LayeredArchitecture...6 Pros([1],LayeredArchitecturalStyle)...6 Cons...7 Example...7 Pros...7 Cons...8 Example OracleDiscovererTool...8 ComponentBasedArchitecture...8 Pros...10 Cons...10 Example Gaming...10 ThenandNow:...10 InheritanceBasedProgramming:...10 CBAtotheRescue:...11 References...11

3 Introduction)to)Software)Architectural)Styles) Softwarearchitecturalstylesarepatternsorframeworksthathavebeendevelopedas generalsolutions tocommonproblemsthatariseinthesoftwaredevelopment process.theygenerallyspecifyordefinethecomponentsandconnectorsthatcompose asolutionandtheirrelations program. Message)Bus)Architecture) Themessagebusarchitectureisamessageorientedmiddlewareapproachto centralizingcommunicationwithinanapplication(orbetweenaseriesofthem).analogousto thehardwarebusarchitectureusedtolinkphysicalcomputerresources,themessagebus offersroutingandmessagepassingsupportbetweensoftwaresystemsorsubsystems.itis looselycoupledtothecomponentswhichutilizeit,asitoperatesindependentoftheir implementationsolongastheymatchtheinterface[22]. basedformsofthepublishandsubscribearchitecture listandbroadcast lendthemselves informationonthebus itmaintainsalistofsubscribersforeachtopic,andwhenevera messageispassedtothebus,thebuswillcopyandsendthemessagetoeverysubscriberofthe sideoftherelationship.amessagesenttothebusisforwardedindiscriminatelytoall connectednodes,andmessagesofunwantedtopicsaresimplyfilteredoutandignoredbythe recipientapplications[23]. Serviceorientedarchitecturelendsitselfverywelltoutilizingamessagebus architecture facilitatingthesubscriptionofserviceproviderstoservicerequesters[24].by providingaserviceregistryandrepository,themessagebuscanpermitnumerousandhighly variedservicestoserveeachotherwithoutneedingextensiveconnectionlogicintherespective serviceapplications. Pros:) Improved)Modifiability[21] Applicationsaddedtoorremovedfromthesystemnolonger affectanyothercomponents;solongastheyfollowthemessagebusspecificationsintegration withothercomponentsisseamless.newmessagescanbeaddedwithoutbreakingoldones. Objectsofanytypecanbeencapsulatedanddeliveredviathebus[22].

4 Reduced)Complexity[21] Messagesendersnowonlyinteractwiththebusinsteadofall messagerecipients;likewise,themessagerecipientsneedonlyinteractwiththebusinsteadof allsenders. Improved)Performance[21] Withallroutingandmessagepassinghandledbythebus, performanceisboundtobuscapacityandthroughputandfreedfromtheconstraintsof potentiallyhaphazardmessagepassingprotocols. Improved)Scalability)[21] AddingadditionalservicesorapplicationstothebusisanO(1) operation,limitedonlybythecapacityoftheimplementedbus. Cons:) Increased)Complexity[21] Integrationbecomesmorecomplexwithamessagebusbecause allcomponentsaccessingthebusmustbeshapedtofititsintegration.additionally,itisa sharedresourceandmustaddressconcurrencyandqueuingconcerns. Lowered)Modifiability[21] Changestothebusinterfacemustmaintainbackwards compatibility,oreverycomponentthatutilizesthebuswillhavetobeupdatedinorderto supportthenewinterface. Lowered)Security)[21] Abroadcastbasedmessagebusoffersnoprivacywithoutsomeform ofencryption,asmessagesaredeliveredindiscriminatelytoallconnectednodes.[23] Low)Downtown)Tolerance)[21] Thebusbecomesasinglepointoffailureforall communicationacrosstheapplication(s).logicisnotnecessarilyimplementedforapplications tomanagetheirownmessageswhilethebusisoutofservice,whichcanleadtomessageloss andfailuresofdataintegrity. Example) )DJBus) utilizesthemessagebusarchitecture.itconsistsprimarilyof:[19] communication Themessagebusdaemon,whichcanconnecttomanysimultaneousapplicationsand providesrouting Bindingstofacilitateawidervarietyofframeworksandsystems

5 facilitatetheseconcerns. [25]% %The%D+Bus%Concept%Diagram%

6 Client)/)Server)Architecture) entityonthenetworkassumestheroleofeitheraclientoraserver.serversarepowerful computersorprocessesdedicatedtomanagingasetofresources([17],page18).theyare ideallyactiveatalltimestoservicerequestsmadebyclientsinordertoprovideasetof resourcesorfunctionalities.serverscanservicemanyclientsatatimeandregulatetheir access([18],page261).aclientisasingleuserhostsystemsuchasapcorworkstationwith userapplicationsthatinitiatecontactwiththeserverinordertomakeuseofitsresources([17], page10).theseresourcescanincludedata,cpu s,printers,anddatastoragedevices.clients nevercommunicatedirectlywitheachother;theyareonlycapableofindirectcommunication throughtheserver.clientsandserversarelocatedphysicallyondifferentcomputersystems andrequireremoteaccesstocommunicate([18],page261).clientsandserversareloosely serversoftwareisindependentofhardwareoroperatingsystemplatforms. processing,anddatamanagementfunctionsarelogicallyseparated.fatclientreferstoclients foralotofthecomputationsandprocessesthatareneededtoperformaparticulartaskwhile theserverisresponsibleforverylittle.incontrast,thereisathinclientinwhichtheserveris responsibleforavastmajorityoftheworkandtheclienthasverylittleresponsibility([18],page Pros)([13])) Centralization)of)data:)Alldataisonasingleserver,simplifyingtheorganizationand managementofdata.thisalsomakesiteasiertobackupdataaswellas modifying/editing([17],page12). Security:)Requestsmadebyclientscanbemonitoredandlogged.Validationcanbe enforcedwithrequeststoensurethatonlythoseclientswithvalidcredentialscanhave accesstospecificservices. Cons)([13])) Congestion:)Ifanincreasingnumberofclientswishtocommunicatewiththeserver,this willincreasetheserver sworkload,thusreducingnetworkspeeds. Cost:)Costofsetupandmaintenancearegenerallyhigh. Not)Robust:)Iftheserverfails,theclientswillnolongerbeabletofunction.Clientswill notbeabletointeractatalluntiltheserverisrestored.

7 Example) )Microsoft)SQL)Server) Microsoft ssqlserver.asthenamesuggests,sqlserverisadatabaseapplicationinwhichthe databaseresidesonaserver.theserverisarelativelylargecomputerinacentralizedlocation. Clientscanconnecttotheserverandmakerequestsfordatausinganumberofdifferent applications.havingthedatabasecentralizedonaservermakesitmucheasiertomaintainan uptodatecollectionofdata.clientsdonotneedtocontinuallyupdatelocalcopiesofthe databasetoensureconsistency.sqlserverprovidessecurityoptionsaswell,requiring 5). ObjectJOriented)Architecture) focusesonbreakingdownasystemintoindividualandreusablecomponents,orobjects. Objectstypicallyconsistofdatafields(ie.attributes)andprocedures(ie.methods).Objectsare usuallyinstancesofclasses,andaprogramcanbeconsideredtobeacollectionofobjects interactingwitheachother.thisisincontrasttothemoreconventionalprocedural programming,whereaprogramismorelikealistofsubroutines.objectsareseparate, independententitiesthatarelooselycoupled.theycommunicatewithoneanotherthrough interfaces,methodcalls,andsendingandreceivingmessages. Fundamental)Features)([1],)ObjectKOriented)Architecture)Style) Inheritance:)Objectscaninheritthecharacteristicsofotherobjects.Thismeansan objectcaninheritthefunctionalityofanotherbaseobject,andevenoverridethat functionality sbehaviour.changestoabaseobjectarealsopropagateddowntolower objects. Encapsulation:)Theinternalsofanobjectcanbehiddenfromotherssothatonlythat objectcanmanipulateitsownstateandvariables.thisprotectstheintegrityofthe objectandpreventsusersfromsettingtheinternaldataofthatcomponenttoaninvalid orinconsistentstate. Abstraction:))Abstractionreferstobreakingdownasystemintologicalcomponentsthat canperformsomesortofworkandcommunicatewithotherobjectsinmeaningful ways.itcanhelpreducecomplexity. Polymorphism:)Polymorphismreferstogivinganobjectmultipleforms.Itallowsyouto makechangestoabaseobjectandextendittodifferenttypes,whilestillkeepingthe baseobjectinterchangeablewithitsotherforms.

8 Pros)([1],)ObjectJOriented)Architectural)Style)) Reusable Extensible Morecloselyrelatedtohowweviewworldobjects Increasedcohesion Easiertestingthroughencapsulation Cons) h h h Strongcouplingbetweensuperclassesandsubclasses.Swappingoutsuperclassescan oftenbreaksubclasses. Notallproblemscannecessarilybebrokendownintoclearlydefinedobjects. Notnecessarilyappropriateforsmaller,lesscomplexprojects. Example) )Cocoa)[20,)ModelJViewJController]) Agoodexampleofapracticalapplicationofobject@orientedprogramming(OOP)isApple s nativeapi,cocoa.cocoaisimplementedinobjective@c,anobject@orientedprogramming language.cocoaalsogreatlyemphasizesthemodel@view@controller(mvc)architecture pattern,whichisstronglytiedtotheobject@orientedparadigm. Asthenamesuggests,inMVCtherearethreemainobjects:Model,View,andController.The Modelconsistsoftheapplicationdataandlogic,andtheViewrequestsinformationfromthe Modelanddisplaysitassomevisualrepresentation(ie.GUI).TheControlleractsasan intermediaryobjectandpassesinformationbetweenthemodelandtheview.eachobjectis independentfromtheothers,whichgivesthesystemalotofflexibilityandmakesthe componentshighlyreusable,whichisoneofoop sbiggestadvantages.changestoone componentdonotnecessitatechangestoanother.asimpleexamplewouldbeusingdifferent GUIsforthesamesystem.InthiscaseyoucouldreusethesameModelandController,andonly havetomakechangestotheview,savingalotoftimeandeffort.virtuallyalltheapps developedforapple sappstoresstronglyadheretothisideaofmodularityandreusability. Layered)Architecture) TheLayeredArchitectureStyleisfocusedarounddividingsoftwarefunctionalityintodistinct layersthatinteractvertically.itisdependentonmessagepassingbetweenlayersandclearly

9 definedfunctionallayers.eachlayercanonlysendorreceivemessagestothelayerdirectly aboveorbelowit. Pros)([1],)Layered)Architectural)Style)) Abstraction:Layeredarchitectureabstractstheviewofthesystemaswholewhile providingenoughdetailtounderstandtherolesandresponsibilitiesofindividuallayers andtherelationshipbetweenthem. Encapsulation:Noassumptionsneedtobemadeaboutdatatypes,methodsand properties,orimplementationduringdesign,asthesefeaturesarenotexposedatlayer boundaries. Clearly)defined)functional)layers:Theseparationbetweenfunctionalityineachlayeris clear. Upperlayerssuchasthepresentationlayersendcommandstolowerlayers,suchasthe businessanddatalayers,andmayreacttoeventsintheselayers,allowingdatatoflow bothupanddownbetweenthelayers. eachlayercontainsfunctionalitydirectlyrelatedtothetasksofthatlayer,willhelpto maximizecohesionwithinthelayer. Reusable:Lowerlayershavenodependenciesonhigherlayers,potentiallyallowing themtobereusableinotherscenarios. Loose)coupling:Communicationbetweenlayersisbasedonabstractionandeventsto provideloosecouplingbetweenlayers. Design)Pattern)Support:Thelayeredarchitectureissupportedbymanysoftwaredesign patternsincludingmvcandotherseparatedpresentationpatterns. Cons) Theonlymajordisadvantageinvolvedinlayeredarchitectureinvolvedifficultiesstructuring systemsaslayeredsystems.specifically,restrictingcommunicationtoadjacentlayers,and keepingcouplingbetweenlayersreduced.([2],page12)ifsoftwaresystemscanbesuccessfully designedaslayeredsystems,therearenodisadvantages. Example)) Anexampleofalayeredsoftwaresystemisthisprocesscontrolforchemicalproduction processes.theleftsiderepresentsthesoftwareside,andtherightrepresentsthehardware side.

10 ImageSource:[2],page28 Level1:Processmeasurementandcontrol:directadjustmentoffinal controlelements. Level2:Processsupervision:operationsconsoleformonitoringand controllinglevel1. includingmanagementreports,optimizationstrategies,andguidanceto operationsconsole. functionssuchascostaccounting,inventorycontrol,andorder processing/scheduling.

11 NJTier)Architecture) tiers.eachtiercanbelocatedonaseparatephysicalcomputer.thesesystemsare ofmessagepassing.eachtierinthesystemiscompletelyindependentfromalltiers exceptthoseimmediatelyaboveandbelowit.communicationbetweenthetiersisnot ArchitecturalStyle) becauseinitsmostcommonincarnationtherearethreetiers,eachlocatedona tiestothelayeredarchitecturalstyle,andtheymaybeusedatthesametimeinwhich inquestionrequiresanamountofresourcesthatcouldleadtodecreasedperformance ofothercomponentsofthesystemifitweretoberunonthesamemachine.itisalso usedifalayerneedsaccesstosensitiveinformationwhichisnotneededinotherlayers, asitallowsthedatatobestoredinaplacewherenootherlayerscanpossiblyaccessit. Pros)([1],)NJTier/3JTier)Architectural)Style)) Maintainability Eachtierisindependentoftheothertiers,whichallowschangesandpatchestobe performedonapartofthesystemwithoutaffectingtheapplicationasawhole. Maintainabilityisanextremelyimportantconsiderationinanysoftwareproject,sothis isalargebenefit. Scalability Becausetiersaredesignedbasedontheapplication slayers,scalingtiersisasimple importantbenefit. Flexibility Sinceeachtierismostlyindependent,theycanbemanagedorchangedindependently, allowingforaflexibleapplication. Availability Sinceatierisresponsibleforonecomponent,itiseasyfortheapplicationtoincrease theamountofacertaincomponent,allowinghigheravailability.

12 Cons)([4],)Goals)of)a)Good)NJTier)Application)) Bloat Sincecommunicationbetweentiersisneededandtheyareondifferentmachines, programscanbecomemuchlargerthantheyotherwisewouldbe. Inflexibility therearesomeinstancesinwhichhavingtocommunicatebetweenmultiplelayers necessitatesdatabeaccessedinaspecificwaywhichmightnotbewhatiswanted. Example) )Oracle)Discoverer)Tool)([5],)1.2.1)) sdiscoverertool.itisan

13 Component)Based)Architecture) ComponentBasedArchitecture(CBA)isanarchitecturethatfocusesondecomposing softwaredesignsintofunctionalorlogicalcomponentswiththeirownmethods,events andproperties.thecomponentsarelooselycoupledandreusabletoprovidemodular programsthatcanbetailoredtofitanyneed.assuchthecbacanprovidealevelof abstractionhigherthanthatofobjectorientedprogrammingarchitecture(oopa)and doesnotfocusonissuessuchascommunicationprotocolsandsharedstate. Components:) Acomponentcanbeanysoftwarepackage,webserviceormodulethatencapsulatesa relatedsetoffunctionsordata([6],softwarecomponentarchitecture).theideaisto havethecomponentfullyencapsulatedtothepointthatonecanmakefulluseofsaid componentwithoutrequiringknowledgeofitsimplementation.itprovidesthis functionalitytotherestofthesystembyuseofaprovided%interface.aprovided interfacespecifieswhatacomponentcanprovidetoothercomponentsinthesystem. functions. Theideaofallthisistodevelopthesoftwarecomponentstothepointofbeing independentorloosely%coupledwithothercomponentsinthesystem.inanideal scenariotheonlythingacomponentshouldrequiretooperateisasystemmechanism thatprovidesanenvironmentinwhichthecomponent(s)canexecute.whilethisideal, itisnotalwayspossibleandassuchcomponentscandependonothercomponentsto executebyadoptingaused%interface.ausedinterfacespecifieswhatacomponents needstooperate. Pros)([7],)What)are)the)advantages)and)disadvantages)of)plugJin)based) architecture?)) Ease)of)deployment.Asnewcompatibleversionsbecomeavailable,youcanreplace existingversionswithnoimpactontheothercomponentsorthesystemasawhole. developmentandmaintenance.

14 definedfunctionality,allowingdevelopmentwithoutimpactingotherpartsofthe system. Reusable.Theuseofreusablecomponentsmeansthattheycanbeusedtospreadthe developmentandmaintenancecostacrossseveralapplicationsorsystems. Mitigation)of)technical)complexity.Componentsmitigatecomplexitythroughtheuseof acomponentcontaineranditsservices.examplecomponentservicesinclude componentactivation,lifetimemanagement,methodqueuing,eventing,and transactions. Cons) Message)Handling)needstobepredefinedforthecomponents.Possibilityitcouldbea limitingfactor. Reliance)on)Third)Parties.Ifyourcomponentscomefromathirdpartyofsomesort thenyouwillbeattheirmercyforupdatesandchangestothecomponent. Complexity.)Whileitisdesignedtoreducecomplexityofsystemsitintroducesa someproblemsmayonlysurfacewithcertaincombinationsofcomponents. Testing.)Canbedifficultifthecomponentdoesn tcomewithit sownexecution environment.(moreofathirdpartycomponentproblem) Second)System)Syndrome.)Dependingonhowcomplexthecomponentsthemselvesare youcanendupwithaplatformwithinaplatformwithinaplatformtypeproblem. Example) )Gaming) ThenandNow:) DoomandQuake.Youknowthesenames.Iknowyoudo.Backinthedayyouweren ta personunlessyouhadexperiencedthemajestythatisdoomandquake.whilenot beingknownforhavingalotof contentdepth buttheywereknownforhavingmany thingstokill.theywerehoweverknownforbeingattheveryforefrontofgame programmingtechnology.adaptivetilerefresh,raycasting,binaryspacepartitioning (whichdoombecamethefirstgametouse),andsurfacecaching(whichwasinvented forquake)%wereallprogrammingtechniquesthatwereeitherfirstpioneeredoreven (everythingelsewasc/c++orsomesortofasm).thesegameswereparagonsoftheir kind Flashforwardtotoday sgamingeraandwefindweareinaverydifferentplace.games arenowmassive,extremelyresourceintensiveprograms.theycanmeasureonthe

15 scaleof25gbforasingletitleandcanofferaseeminglyendlesspitofcontent,depth andevenmorethingstokill.sufficeittosaygamestodayarecomplex.verycomplex. Andthereinisourproblem.AlotoftheOOprogrammingtechniquesusedbygames backinthedayarenolongerfeasibleanymore.thebiggestoftheseoffendersis InheritanceBasedProgramming([9],PreferCompositionoverInheritance[Online]). InheritanceBasedProgramming:) WhatisIBP?Wellit slikethis.let ssayyouhaveachestobjectinagame.thechestis,let s say,aderivedclassofacontainerwhichisaderivedclassofagenericgameobject. Thisisprettystraightforwardandwouldhaveyieldedaperfectlygoodchesttouseandbackin thedaythiswouldhavebeenawesome.nottoday.todaygamerswillnotbesatisfiedwitha simplechestthatsimplyopensandclosesallsimplechestlike.no,theywantthatchestto attackthemorfollowthemaroundlikeasidekickmakingwittyremarkseverynowandagain. Theproblemisthatnoneoftheobjectsinourchesthierarchyhaveanyfunctions,methodsor parametersformakingthechestanentityormovable.soweneedtoadditbyattaching anotherhierarchy.

16 Sonowwehaveachestwithmultipleinheritancesoitcanbeachestthatmoves.Simpleon paper,veryhardtoimplement,andimpossibletodebug(handcrafting).sohowdowefixthis? CBAtotheRescue:) WecanfixitwithaproperapplicationofCBA.IfweuseCBAwecanalleviatebyaddingproper concessionsintothegenericgameobjectclass([10],componentbasedgamearchitecture)to acceptnewcomponentstoletthechestmovewithoutrequiringmultipleinheritance.thislets usinessencecreateaverycomplexgamewithoutusingverycomplexmethods.thegame engineitselfbecomeseasiertomanagebecauseitwasbuiltwithourlooselycoupled,modular parts. Conclusion Asdiscussedabove,therearemanyarchitecturestylesthatcanbeusedwhendesigning software.thetypeofarchitecturethatisbestforagivenprogramdependsonthetypeof softwarethatisbeingdevelopedandthestylethatdevelopersaremostconfidentinusing.

17 References) [1]Microsoft.(2013).Chapter%3:%Architectural%Patterns%and%Styles[Online].Available: [2]D.GarlanandM.Shaw.(1994).AnIntroductiontoSoftwareArchitecture[Online].Available Pdf: [3]J.Booth,BuildingMiddleTierObjectsinVisualFoxpro[Online].Available: [5]OracleCorporation,OverviewofOracle9iASDiscoverer[Online].Available: [6]RainerNiekamp.SoftwareComponentArchitecture[PDF].Available: [9]SteffenItterheim(2010,June11).PreferCompositionoverInheritance[Online]. [10]JordanSpringett(2012,Feb16).ComponentBasedGameArchitecture[Online].Available: [12]Lexus.(2011,March20).ProsAndConsofDistributedClient/serverArchitectures[Online]. Available: architectures

18 [14]Microsoft.SQLServerOverview[Online].Available: [16]M.I.JawidNazir.ClientServerComputingIntroduction[PDF].Available: [17]S.H.Kaisler.(2005).SoftwareParadigms[PDF].Available: [19]Apple.(2012).Concepts%in%Objective+C%Programming[Online].Available: pedia/introduction/introduction.html [20]Microsoft MessageBus[Online].Available: [21]Tody,Doug.(1998).MessageBusandDistributedObjectTechnology[Online].Available: [22]Microsoft Publish/Subscribe[Online].Available: Available: