Mapping of QoS-Enriched Models to a Generic Resource Model

1 UniversityofOsloDepartmentofInformaticsM appingofQoS-EnrichedModelstoa stituteofInformatics, wanttothankmysupervisors,Jan yvindAagedalandArnorSolberg, DrivenDevelopment.. les.. cationofQoSCharacteristics.. cation.. ManagementinMiddleware.. AwareComponentArchitecture..274 CONTENTS53 QoSinModel cationinModels.. IndependentQoS.. TimeSupportforQoSinMDA.. TimeResources.. leforQoS.. leImplementation.. leforResourceModeling..596 CONTENTS5 Model .. EnrichedModels.. ServiceandModel-DrivenDevelop-mentModel drivendevelopment(MDD) hasgaineda lotofattention,especiallyinconjunctionwi thsoftwaredevelopmentformiddlewareplatfo rmssuchasCORBA,Java2 Enter ,code centricdevelopment,thecreatingmodelsis typic allymerelya drivendevelopment,themodelsareintendedto become rst classen tities, (MDA)[21] isanapproachtomodel drivendevelopmentproposedbytheObjectMana gementGroup,andusestheUni edModelingLanguage[25] independentmodel(PIM)andtheplatform speci cmodel(PSM).A PIMthedevelopershouldonlyhavetoworryabou tthebusinesslogicoftheapplication,asoppo sedtoplatform speci cim (throughprede nedmappings) PSMcanalsobeconsidereda kindofmodeltransformation,wherethecode78 Chapter1.

2 Introductionis considereda ableorcouldneedre ,theUMLdoesnotincludethenecessarysemanti cstocreatefullyexecut (QoS)dealswithqualitativepropertiesofser vicesprovidedbya ,throughquantitativemeasures(likelatency andthroughput),otherscanonlybemeasuredsu bjectivelybyhumans(suchaslearnability).Q oSrequire mentsdi ersfromthefunctionalrequirementsofa notconcernedwithwhatfunctionsa systemcanperform, [3] it is edearlyinthedevelopmentprocess,becauseth eyaredi culttomanageafterthesystemis ortis ,componentarchi awareComponentArchitecture(QuA)platform[ 29] isonesuchplatformde velopedaspartofa jectlooksintohowaserviceplannercanrealiz ea certainlevelofQoSbyselectingappropriatec ompositionsandcon a low levelfactorthathelpsdeterminewhatlevelof QoSthesystemis , re sourcemodelprovidesanabstractionofthecon creteresourcesinthesystem,andservesasa resourcemodelcanbeincorporatedinQoS enabled, Model runtime generalde nitionofresourcefromBritannicadictionary is: Asourceofsupplyandsupport.

3 Weneedtospecializethisde ,it doesnotmentionthatresourcemustbelim , fectlyunderanycondition, isnotourintentiontomodelallthinkablereso urcesintheworld, ,wedealonlywithresourcesusablewithina leforSchedulability,PerformanceandTime[2 4] de nesa resourceinstanceas arun timeentitythato ersoneormoreservicesforwhichweneedtoexpr essa measureofe ectivenessorqualityofservice(QoS) . Thisde nitionimpliesthatresourcesprovidea limitedlevelofQualityofService,thushavin ga methodforhandlingQualityofServicecon cernsina Model levelQoSrequirementscanbetreatedina Model drivendevelopmentprocess,fromdesign timeQoSspeci cationtorun ndoutwhetherourapproachis feasible,wewillinvestigatethefollowing: HowresourceQoSrequirementscanbemodeledat design timeina waysuchthattheycanbeconsideredlaterinthe developmentprocess. HowtotransformtheresourceQoSrequirements expressedinthemodeltoa formthatis manageablebythetargetplatform. Howa resourcemodelcanbedesignedandimplemented ona tar getplatformin ordertosupportsmappingofresourceQoSrequi re edaspartoftheapplicationmodel,andthatthe serequirementscanbeautomatic allytransformedandmappedtotheresourcemod eloftheimplementa cationandspeci cationofQoSat design time,andeasetheimplementationofQoS ,anddiscusshowtheapproachproposedinthist hesis nea genericresourcemodelwithsupportformodeld rivendevelopmentandmiddleware a platform spe ci drivendevelopmentis bymanypredictedtobethenextbigleapin thesoftwaredevelopmentindustry, (OMG)hasproposedModelDrivenArchitecture( MDA)astheirapproachtomodel drivendevelop de nesmodel drivenas"providinga meansforusingmodelstodirectthecourseofun derstanding,design,construction,deployme nt,operation,maintenanceandmodi cation"[21].

4 AnimportantadvantageofMDAis theseparationofimplementationde tailsfrombusinessconcerns[8].Bymakingbus inessmodelinga separ ateactivity, ,thesamemodelcouldbedeployedondi erentplat forms,thusbettersupportingchangesintechn ologyovertime, [16].A modelcanrepres entvirtuallyanysystem, modelis in [32] de nedasa setof statementsaboutsomesystemunderstudy. It mentionstwopurposesa rstpurposeis adescription, tryingtodescribea systemalreadyinexistence,andthesecondis aspeci cation, thatstateshowthemodelerwantsthesystem111 2 Chapter2. ,modelsmustbecreatedina modelinglan ,modelsarepresenteda combinationofdrawingsandtext[21]. TheUni edModelingLanguage(UML)[25] is thedefaultlan guageinMDA,anda deffactostandardforobject orientedsystemsis themostcommonapplicationofUML,it is a modelofa ,ontheotherhand,isnotself cordingto[32], a metamodelmakesstatementsaboutwhatcanbeex pressedinthevalidmodelsofa ,theymeanthatmetamodelsdescribehowmodels canbeconstrcutedbyde nition tswellwiththede nitionintheMeta ObjectFacilityspeci cation[9]:A metamodelis an abstractlanguage fordescribingdi erentkindsofdata.

5 Thatis,a languagewithouta cationofUML[25] is sucha metamodel,andthus, ObjectFacility(MOF)[9]fromOMGcontainsa cation,forexample,isde ,MOFmodelsmayconsistofclasses,attributes ,datatypes,packages, ,a MOFclasswilltypicallyrepresenta speci cgraphicalnotation,a cationincludesa separationoffourmetalevelsformod metamodelsM2 MetamodelsM1 ModelsM0 InformationMeta metamodelsaremodelsofmetamodels,andcanbe seenasa lan netheabstractlan thesystemspeci edbysystems,forexamplerecordsina basedMetadataInterchange(XMI)[26] is ,andarethere cation,includingbothmodelandmetamodelinf ormation[26]. AswellasMOFmetamod els,theXMIformatcanbeusedtostoreanymodel ofwhichMOFis typicalusageofXMIis a general purposelanguage,it maynotbesuitableformod elingwithinparticulardomains[19]. UMLprovidesa setoflight lesarein[6] describedasa pro leistypicallytailoredtowardsa particularapplicationdomainorimplementat ionplatform,wheretheUMLextensionsre ectdomain speci corapplication speci pro leis a groupingofUMLextensions, ingtheseelementsin a Model ,themodelermayapplytheavailable14 Chapter2.

6 Stereotypeisintendedtogivetheelementanex tendedmeaningwithoutrede ,ina UMLpro leforrelationdatabases,atablecouldbemode ledasa classwithstereotype Table .Taggedvaluesareattributesrelatedtoa a leswere rstintroducedin [6] asa setofguidelinesforhowtoimplementUMLpro moreprecisede nitionofpro , ,asit is notyet nalizedbytheOMG,andthetoolsupportattheti meofwritingis lesarea light weightalternativetode ninga completelynewdomain speci clanguage( ,byde ninga newMOFmetamodel).SincetheUMLmetamodelmus tberespectedwhende ningpro les, ,pro lesareless exiblethande ninga exibilityis a typicaltrade o whende ningnewmodelinglanguagesandchoosingbetwe ena UMLpro leanda newmetamodel[19].Inordertode nea UMLpro le,the rststepis tocreatea modeloftheelementthatcompriseourplatform orsystem,andtherelationshipsbetweenthem[ 19]. Thistypeofmodelis referedtoasadomainview pointorconceptualmodel. In ordertousetheseconceptsin Models , de nedinanothermodel,oftencalledtheUMLviewp oint. [4]it is arguedthatUMLpro lesprovideonlycontent,andnotform(linguis ticrelationships).

7 Therefore,thedomainviewpointofUMLpro lesis notalinguisticmetamodellikethemetamodelo fUML, [19] it is claimedthatUMLpro leshavea thetransform ationbetweenPIMsandPSMs,andUMLpro lesareverywellsuitedtorepresentplatform speci [21] de nesmodeltransformationas"theprocessofcon vertingonemodeltoanothermodelofthesamesy stem". InMDA,thesourcemodelofthetransformationi s typicallya PIM,andthetargetmodelisa modeltransformationtakenfrom[21] is showninFig showsa transformationfroma PIMtoa [33]modeltransformationis de nedas"automatedprocessesthattakeoneormor esourcemodelsasinputandproduceoneormoret argetmod elsasoutput,whilefollowinga setoftransformationrules". Thisde ni ,theMDAalsoallowsmanualorsemi manualtransformationsofmodels[21]. ortbyOMGtostand ardizehowtospecifymodeltransformationsby de ninga nedin16 Chapter2. ,atransformationfroma sourcemodeltoa targetmodelis representedinQVTasa [12] it is arguedthatprogrammerstypicallyneedtoachi evethesamefunctionalityindi erentplaces,andbuildingcodegeneratorsis anef specialkindofcodegenerationismodel to codetransformation, wherecodeis generatedbasedona ,thePSMisa typicalsourcemodelforgeneratingplatform speci ,ora requestforproposalforaMOFM odeltoTextTransformationLanguage[22].

8 It aimstoprovidea languagefortrans formingMOFmodels(suchasUMLmodels) thetransformationofPIMsandPSMstocode,XMI ,human readableUMLformat,documentation, ardomg:qvtdoesnotaddressmodel to codetransformations,thisRFPseeksto is arguedin[22]thatXSLTis nota supportstransforminganXMImodel,thetransf ormationcodewillbecomplexanddi (QoS)isinOpenDistributedProcessing ReferenceModel QualityofService[15] de nedas: ageneraltermforanab stractioncoveringaspectsofthenon functionalbehaviourofa system. Functionalbehaviouris theactualfunctionalityo eredbythesystem,whilenon functionalbehaviourdescribeshowwellthisf unctionalityiscarriedoutPerformanceandla tencyareexamplesofnon functionalas basicentityin[15], It representsanaspectofQoSasopposedtoa measure anexpressionthatinvolvesoneormoreQoSchar acteristicsandoneormorevalues,wheretheva lue(s) , ,therealizationoftheserequirementsis straight forward,giventhattheresourcesprovidesu (suchasapplicationsorservices)ratherthan re lesstrivial, ,thesekindsofrequirementsimplicitlyleadt olower levelrequirements( ).

9 Ap plicationQoSis a commonnamefornon functionalrequirementsofap ively, , orperceivedQoS, involvesevenmoreabstractQoSrequire ceivethequalityofa service(forexample, thevideoshouldhaveasharppicturewithgoods oundquality ).Thiskindofrequirementiseasytounderstan dforthenon technicaluser,butdoesnotmapeasilytotheim plementationthatis edintodi icaldomainsthatdealwithQoSrequirementsar emultimedia,real timesystems, system,theQoSmustbespeci cationcanbedoneatdi erentdomainsandabstractionlevels,18 Chapter2. Backgroundandcanbeexpressedin di erentspeci [16] it is ar guedthatQoSspeci cationis importantinseveraldevelopmentphases, cationwemeantheactivityofmakingstatement saboutQoSina formalwayusinga speci weallowedin formalQoSspeci cation( ),a (CQML)isspeci [16].It is a genericQoSspeci cationlanguage,nottiedtophaseofthesoftwa relife cycleoranyspeci isa declarativelanguage, [16] ,suchasQoScharacteristic, fromtheISOQoSframe work[13].QoScharacteristics(QoScharacter isticsinCQML)areuser de nedtypesthatde nehowa certaintypeofQoSis , acteristics,andQoSstatementscanbegrouped intoQoSpro pro lecanfurtherbeassociatedwitha componentspeci ,aQoSstatementmayrefertooneormoreQoSchar acteristicsandputa mechanismtogroupQoScharacteristics,QoSst ate mentsandQoSpro QoScategoryistimeliness, speci cationcalledUMLPro leforQualityofServiceandFaultToler anceCharacteristicsandMechanismsis currentlyunder workingdocumentofSeptember2004[23] cationprovidesa frameworkforthedescriptionofQoSrequireme ntsandproperties,aswellasa nesthemetamodeloftheQoSmodelinglanguaget hatis supportedbytheUMLpro le,asthisis leforQoSsupportsapplyingnon ,sothatthefunctionalspeci cationofthesystemwillnotbea ectedbynon lesup portsboththespeci cationofQoScharacteristics( ,howQoScanbemeasured)andQoSconstraints( ,whatQoSis required).

10 QoSCharacteristicsaremodelelementsthatre presentquanti ableas edbyoneormoreQoSDi mensions. A QoScharacteristicis de nedindependentlyofthevaluesitquanti ,a QoScharacteristichasoneormoreQoSvalues, representedasa , suchasInteger,Real,andEnumeration. Aswellasthisvalue,QoScharacteristicsared escribedbysometaggedvalues:20 Chapter2. <<QoSCharacteristic>>throughput<<QoSCharacteristic>>latency<<QoSDimension>>{unit(bit/s),direction(icreasing)}+rate : integer<<QoSDimension>>{unit(ms),direction(decreasing)}+averag e-delay : real<<QoSDimension>>{unit(ms),direction(decreasing)}+jitter : realdirectionexpresseswhetherhighervalue srepresenthigherqualitythanlowervalues(i ncreasing),orhighervaluesrepresentlowerq uality(decreasing). eris usedtoexpressstatisticalthattheQoSdimens ionrepresentsstatisticalproperties, ,mean,maximumandmin , withanincreasingdirectionandis ,whicharemodeledasUMLpackageswithstereot ype QoSCategory . A QoScategorytyp icallycontainsQoScharacteristicsofthesam edomain,anddescribedi ,theQoScataloguepresentedin[23] containscategorieslikePerformanceandDepe ndabil speci cquanti cationofa QoScharacteristic,andis containsa xedvaluede limittheallowedvaluesofoneormoreQoSchara cterist ics[23].