《软件体系结构》课件 13-体系结构评估

软件体系结构评估Software

Architecture

Evaluation软件体系结构课程组目录体系结构评估1ATAM2Howdoweknowthatourarchitectureisappropriateforitsintendedpurpose?Inalargedevelopmentproject,anenormousamountofmoneymayberidingon（取决于）thearchitecture.Thefutureofcompanymaybeatstake（危险）.Weneedtoevaluatethearchitecture（评估体系结构）.体系结构评估-Now

what满足需求开发成本潜在危机体系结构评估Architectureevaluationisadevelopmentlife-cycleactivitywherebyseveralstakeholders（项目干系人）

analyzethesoftwarearchitecturetogetherinaformalorinformal（正式或非正式）

processusinganassessmenttechniquesuchasscenarios（场景）.体系结构评估-定义EarlydetectionofproblemswiththeexistingarchitectureTheearlierinthelifecyclethatproblemsaredetected,thecheaperitistofixthem.ValidationofrequirementsArchitectureevaluationsuncovertheconflictsandtradeoffs,andprovideaforumfortheirnegotiatedresolutionForcedpreparationforthereviewManysystemsdonothaveanarchitecturethatisunderstandabletoalldevelopers.Theprocessofpreparingfortheevaluationwillrevealmanyoftheseproblems.Improved

architectures体系结构评估-whyThiswasprobablythefirstdocumentedsoftwarearchitectureanalysismethodandwasoriginallydevelopedtoanalyzeanarchitectureformodifiability.However,itisusefulforanalyzinganynonfunctionalaspectofanarchitecture.Itisfoundedontheuseofstakeholder-generatedscenariostoassessanarchitecture.Scenario-basedArchitectureAnalysisMethod(SAAM)体系结构评估-评估方法ThisisasuccessorofSAAMandisalsogainingwidespreaduse.Thismethodincorporatesqualityattributeutilitytreesandqualityattributecategoriesintheanalysisofanarchitecture.WhereasSAAMdoesnotexplicitlyaddresstheinteractionsbetweenqualityattributes,ATAMdoes.Thus,thetrade-offsarewithrespecttocompetingqualityattributes.ATAMisaspecializationofSAAM,specificallyfocusingonmodifiability,performance,availability,andsecurity.ArchitectureTrade-offAnalysisMethod(ATAM)体系结构评估-评估方法Thismethodconsidersthecomplexityofevaluationscenariosasthemostimportantriskassessmentfactor.SAAMFoundedonComplexScenarios(SAAMCS)Thismethodfocusesspecificallyonthequalityattributesofevolution（演化）

andreusability.ThismethodintegratesSAAMwithdomain-specific

andreuse-basedsoftwaredevelopmentprocesses.ExtendingSAAMbyIntegrationintheDomain(ESAAMI)SoftwareArchitectureAnalysisMethodforEvolutionandReusability(SAAMER)体系结构评估-评估方法Thismethodutilizesscenarios,simulation（仿真）,mathematicalmodeling,andexperience-basedreasoning（基于经验的推理）forassessingqualityattributes.Thismethodalsoincorporatesanarchitecturedesignmethod.Scenario-BasedArchitectureReengineering(SBAR)Thisisanothermethodforanalyzingmaintainabilityusingscenarios,calledchangescenarios,whichrepresentmaintenancetasks.（体系结构级别上的软件维护预测）ArchitectureLevelPredictionofSoftwareMaintenance（ALPSM）Thismethodisbasedonformalandrigorous（严格精确的）qualityrequirements.SoftwareArchitectureEvaluationModel(SAEM）体系结构评估-评估方法目录体系结构评估1ATAM2TheATAMisamethodthathelpsstakeholdersasktherightquestionstodiscoverpotentiallyproblematicarchitecturaldecisions.Tradeoffs（折衷）canbeexplicitlyidentifiedanddocumented.Discoveredriskscanthenbemadethefocusofmitigation（减轻）activities:e.g.furtherdesign,furtheranalysis,prototyping.ATAM-概述ThepurposeoftheATAMisNOTtoprovidepreciseanalyses...thepurposeIStodiscoverriskscreatedbyarchitecturaldecisions.Wewanttofindtrends:correlationbetweenarchitecturaldecisionsandpredictionsofsystemproperties.ATAM-目标ThereareanumberofbenefitsfromperformingATAMevaluationsidentifiedrisksclarifiedqualityattributerequirementsimprovedarchitecturedocumentationdocumentedbasisforarchitecturaldecisionsincreasedcommunicationamongstakeholdersTheresultsareimprovedarchitectures.ATAM-BenefitsATAM的参与人员要求以下三类人员的参与和合作

评估小组Eachevaluationteamconsistsofaleaderandatleastthreeotherteammembers.ATAMteammembersmustbeexperiencedarchitects.ATAMleadersmusthaveexcellentcommunicationandfacilitationskills.项目决策者能够控制程序开发过程和授权变更的人员。通常包含项目经理，为开发买单的用户，和体系结构开发人员构架涉众涉众是与要开发的系统相关的一切人和事。体系结构对可修改性、安全性等质量属性的支持程度会直接影响到涉众人员的正常工作的进行。涉众不等于用户，通常意义的user是指系统的使用者，这仅是涉众中的一部分。涉众通常包括开发者，测试人员，集成人员，系统维护者，性能工程师，用户等等。ATAM-评估小组评估小组的角色角色职责理想的人员素质评估小组负责人准备评估…善于协调…评估负责人负责评估工作…能在众人面前表现自如…场景书记员将场景写到活动挂图上…未搞清楚某个问题之前坚持要求继续进行讨论…进展书记员记录评估进展情况…对构架理解透彻，能融会贯通快速理解技术问题计时员帮助评估负责人保证评估工作按时进行；…勇于不顾情面中断讨论，宣布时间已到过程观察员记录如何改进评估过程或评估如何偏离了原计划…善于观察和发现问题；熟悉评估过程…过程监督者帮助评估负责人记住并执行评估方法的各个步骤对评估方法的各个步骤非常熟悉；….提问者提出涉众或许未曾想到的关于构架的问题对构架有出色的见解；对涉众需要有敏锐的洞察力…ATAM-评估小组ATAMevaluationsareconductedinfourphasesATAM-评估阶段Thecustomerandasubsetoftheevaluationteamexchangeunderstandingaboutthemethodandthesystemwhosearchitectureistobeevaluated.Anagreementtoperformtheevaluationisworkedout.Acoreevaluationteamisfielded（登场）.Phase0:thisphaseprecedesthetechnicalevaluationATAM-Phase0ATAMevaluationsareconductedinfourphasesATAM-评估阶段Phase1:focusedonelicitingdetailedarchitecturalinformationandanalyzingitinvolvesasmallgroupofpredominantlytechnically-orientedstakeholdersarchitecturecentrictopdownanalysisATAM-Phase1ATAM-Phase1ATAMstepsinbriefTechniquesutilitytree（效用树）generationarchitectureelicitationandanalysisscenariobrainstorming/mappingOutputsarchitecturalapproachesutilitytreeandscenariosrisks,non-risks,sensitivitypoints,andtradeoffs1.

TheevaluationteampresentsanoverviewoftheATAMATAM-Phase1businesscontextforthesystemhigh-levelfunctionalrequirementshigh-levelqualityattributerequirementsarchitecturaldrivers:qualityattributesthat“shape”thearchitecturecriticalrequirements:qualityattributesmostcentraltothesystem’ssuccess2.

Thecustomerdescribesbusinessdriversofthesystem.ATAM-Phase1technical

constraintssuchasanOS,hardware,ormiddlewareprescribedforuseothersystemswithwhichthesystemmustinteractarchitecturalapproachesusedtoaddressqualityattributerequirements3.

Designerpresentsanoverviewofthearchitecturedesign.ATAM-Phase1client-server3-tierEventdispatchermechanismpublish-subscriberedundanthardware4.

Identifycorearchitecturalapproaches.Theevaluatorsbegintoidentifyplacesinthearchitecturethatarekeytorealizingqualityattributegoals.ATAM-Phase15.

Identify,prioritize,andrefinethemostimportantqualityattributegoalsbybuildingautilitytree.Autilitytreeisatop-downvehicleforcharacterizingandprioritizingthe“driving”attribute-specificrequirements.（效用树是一个自顶向下的工具，用来刻画重要的需求）UtilityTree？ATAM-Phase1Utility

TreeThedrivingqualityattributesarethehigh-levelnodes(typicallyperformance,modifiability,security,andavailability).Scenariosaretheleavesoftheutilitytree.Output：acharacterizationandaprioritizationofspecificqualityattributePriorityATAM-Phase1ATAMPhase1-PresentArchitecture重要的构架信息4~8张幻灯片上下文图——系统所处的上下文环境；与系统有交互的人或其他系统模块或分层视图——描述系统功能分解的模块（可能是子系统或分层），加上对象，过程，函数及其关系（如过程调用，方法调用，回调，包含等）组件-连接件视图——进程，同步的线程，数据流，连接事件等配置视图——CPUs，存储，外设，传感器网络，通信设备，及在各处理器上运行的进程ATAMPhase1-PresentArchitecture构架方法、模式或采用的战术，包括它们实现了什么质量属性及这些方法如何实现这些属性的描述3~6张幻灯片商业产品（COTS）的使用及其选择/集成1~2张幻灯片对1~3个最重要的用例场景的介绍，如果可能，包括对每个场景的运行时资源使用情况的介绍1~3张幻灯片对1~3个最重要的变更场景的介绍，如果可能，根据所变更的模块或接口来描述变更的影响，即预计的变更的规模/难度1~3张幻灯片与实现促使形成该构架的需求相关的构架问题/风险2~3张幻灯片术语表1张幻灯片ATAMPhase1-GenerateQualityAttributeUtilityTreeIdentify,prioritize,andrefinethemostimportantqualityattributegoalsbybuildingautilitytree.Autilitytreeisatop-downvehicleforcharacterizingandprioritizingthe“driving”attribute-specificrequirements.（效用树是一个自顶向下的工具，用来刻画重要的需求）Thedrivingqualityattributesarethehigh-levelnodes(typicallyperformance,modifiability,security,andavailability).Scenariosaretheleavesoftheutilitytree.Output:acharacterizationandaprioritizationofspecificqualityattributeATAMPhase1-ScenariosScenariosareusedtorepresentstakeholders’interestsunderstandqualityattributerequirementsScenariosshouldcoverarangeofusecasescenarios:anticipatedusesofthesystemgrowthscenarios:anticipatedchangestothesystemexploratoryscenarios:unanticipatedstressestothesystemAgoodscenariomakesclearwhatthestimulusisthatcausesitandwhatresponsesareofinterest.ExampleScenariosUsecasescenarioRemoteuserrequestsadatabasereportviatheWebduringpeakperiodandreceivesitwithin5seconds.GrowthscenarioAddanewdataservertoreducelatencyinscenario1to2.5secondswithin1person-week.ExploratoryscenarioHalfoftheserversgodownduringnormaloperationwithoutaffectingoverallsystemavailability.ScenariosshouldbeasspecificaspossibleStimuli,Environment,ResponsesUseCaseScenarioRemoteuserrequestsadatabasereportviatheWebduringpeakperiodandreceivesitwithin5seconds.GrowthScenarioAddanewdataservertoreducelatencyinscenario1to2.5secondswithin1person-week.ExploratoryScenarioHalfoftheserversgodownduringnormaloperationwithoutaffectingoverallsystemavailability.ATAM-Phase1identifythearchitecturalapproachesaskqualityattributespecificquestionsforhighestpriorityscenariosidentifyandrecordrisksandnon-risks,sensitivitypointsandtradeoffs6.

Evaluationteamprobesarchitecturalapproachesfromthepointofviewofspecificqualityattributestoidentifyrisks.ATAM-Phase1Risks,Tradeoffs,Sensitivities,Non-RisksAsensitivitypointisapropertyofoneormorecomponents(and/orcomponentrelationships)thatiscriticalforachievingaparticularqualityattributeresponse.“Thelevelofconfidentialityinavirtualprivatenetworkmightbesensitivetothenumberofbitsofencryption.”ATAM-敏感点Risks,Tradeoffs,Sensitivities,Non-RisksAtradeoffpointisapropertythataffectsmorethanoneattributeandisasensitivitypointformorethanoneattribute.“Changingthelevelofencryptioncouldhaveasignificantimpactonbothsecurityandperformance.”ATAM-权衡点Risks,Tradeoffs,Sensitivities,Non-RisksAriskisapotentiallyproblematicarchitecturaldecision.“Thelevelofconfidentialityinavirtualprivatenetworkmightbesensitivetothenumberofbitsofencryption.”ATAM-风险决策Risks,Tradeoffs,Sensitivities,Non-RisksNon-risks

aregoodarchitecturaldecisionsthataredeemedsafeuponanalysis.“Assumingmessagearrivalratesofoncepersecond,aprocessingtimeoflessthan30ms,andtheexistenceofonehigherpriorityprocess,a1secondsoftdeadlineseemsreasonable.”（假定消息的到达速率是每秒一次，一次处理的时间小于30ms。如果对一个更高优先级的处理的响应时间要求是1秒钟，此系统可行）ATAM-无风险决策ATAMevaluationsareconductedinfourphasesATAM-阶段ATAM-Phase

2Phase2:involvesalargergroupofstakeholdersPhase2isstakeholdercentricfocusedonelicitingdiversestakeholderpointsofviewandonverificationofthePhase1results.How?Stakeholdersgeneratescenariosusingafacilitatedbrainstormingprocess.Scenariosattheleavesoftheutilitytreeserveasexamplestofacilitatethestep.ATAM-Phase

2Phase2:involvesalargergroupofstakeholdersPhase2isstakeholdercentricfocusedonelicitingdiversestakeholderpointsofviewandonverificationofthePhase1results.Phase

2ATAM-Phase

2Scenariosattheleavesoftheutilitytreeserveasexamplestofacilitatethestep.7.

Stakeholdersgeneratescenariosusingafacilitatedbrainstormingprocess.ATAM-Phase

2Thisstepcontinuestheanalysisstartedinstep6usingthenewscenarios.Continueidentifyingrisksandnon-risks.Continueannotatingarchitecturalinformation.8.

Identifythearchitecturalapproachesimpactedbythescenariosgeneratedinthepreviousstep.ATAM-Phase

2architecturalapproachesutilitytreeScenariosrisksandnon-riskssensitivitypointsandtradeoffsriskthemes9.

Recapitulate（概括）allthestepsofthe