高级软件工程2ppt课件.ppt

Socio technicalSystems社会 技术系统 Objectives Toexplainwhatasocio technicalsystemisandthedistinctionbetweenthisandacomputer basedsystemTointroducetheconceptofemergentsystemproperties系统特性suchasreliabilityandsecurityToexplainsystemengineeringandsystemprocurement获得processesToexplainwhytheorganisationalcontextofasystemaffectsitsdesignanduseTodiscusslegacysystems遗留系统andwhythesearecriticaltomanybusinesses Topicscovered EmergentsystempropertiesSystemsengineeringOrganizations peopleandcomputersystemsLegacysystems Whatisasystem Apurposefulcollectionofinter relatedcomponentsworkingtogethertoachievesomecommonobjective Asystemmayincludesoftware mechanical机械 electricalandelectronichardwareandbeoperatedbypeople SystemcomponentsaredependentonothersystemcomponentsThepropertiesandbehaviourofsystemcomponentsareinextricablyinter mingled混合 Systemcategories系统种类 Technicalcomputer basedsystemsSystemsthatincludehardwareandsoftwarebutwheretheoperatorsandoperationalprocessesarenotnormallyconsideredtobepartofthesystem Thesystemisnotself aware 如 电视 电话 计算机软件Socio technicalsystemsSystemsthatincludetechnicalsystemsbutalsooperationalprocessesandpeoplewhouseandinteractwiththetechnicalsystem Socio technicalsystemsaregovernedbyorganisationalpoliciesandrules 如 一本书从书写到出版构成了一个社会 技术系统 Socio technicalsystemcharacteristics EmergentpropertiesPropertiesofthesystemofawholethatdependonthesystemcomponentsandtheirrelationships Non deterministicTheydonotalwaysproducethesameoutputwhenpresentedwiththesameinputbecausethesystems sbehaviourispartiallydependentonhumanoperators ComplexrelationshipswithorganisationalobjectivesTheextenttowhichthesystemsupportsorganisationalobjectivesdoesnotjustdependonthesystemitself 2 1Emergentproperties系统特性 PropertiesofthesystemasawholeratherthanpropertiesthatcanbederivedfromthepropertiesofcomponentsofasystemEmergentpropertiesareaconsequenceoftherelationshipsbetweensystemcomponentsTheycanthereforeonlybeassessed评定andmeasuredoncethecomponentshavebeenintegratedintoasystem Examplesofemergentproperties Typesofemergentproperty FunctionalpropertiesTheseappearwhenallthepartsofasystemworktogethertoachievesomeobjective Forexample abicyclehasthefunctionalpropertyofbeingatransportationdeviceonceithasbeenassembledfromitscomponents Non functionalemergentpropertiesExamplesarereliability performance safety andsecurity Theserelatetothebehaviourofthesysteminitsoperationalenvironment Theyareoftencriticalforcomputer basedsystemsasfailuretoachievesomeminimaldefinedlevelinthesepropertiesmaymakethesystemunusable Becauseofcomponentinter dependencies faultscanbepropagatedthroughthesystem Systemfailuresoftenoccurbecauseofunforeseeninter relationshipsbetweencomponents Itisprobablyimpossibletoanticipateallpossiblecomponentrelationships Softwarereliabilitymeasuresmaygiveafalsepictureofthesystemreliability Systemreliability可靠性engineering HardwarereliabilityWhatistheprobabilityofahardwarecomponentfailingandhowlongdoesittaketorepairthatcomponent SoftwarereliabilityHowlikelyisitthatasoftwarecomponentwillproduceanincorrectoutput Softwarefailureisusuallydistinctfromhardwarefailureinthatsoftwaredoesnotwearout OperatorreliabilityHowlikelyisitthattheoperatorofasystemwillmakeanerror Influencesonreliability Reliabilityrelationships Hardwarefailurecangeneratespurioussignalsthatareoutsidetherangeofinputsexpectedbythesoftware Softwareerrorscancausealarmstobeactivatedwhichcauseoperatorstressandleadtooperatorerrors Theenvironmentinwhichasystemisinstalledcanaffectitsreliability The shall not properties Propertiessuchasperformanceandreliabilitycanbemeasured However somepropertiesarepropertiesthatthesystemshouldnotexhibit未展现出来的特性Safety thesystemshouldnotbehaveinanunsafeway Security thesystemshouldnotpermitunauthoriseduse Measuringorassessingthesepropertiesisveryhard 如 系统被入侵之后才发现安全性缺陷 2 2Systemsengineering Specifying描述 designing设计 implementing实现 validating有效性验证 deploying实施andmaintaining维护socio technicalsystems Concernedwith考虑theservicesprovidedbythesystem constraintsonitsconstructionandoperationandthewaysinwhichitisused 对于软件工程师来说 有必要了解 系统工程知识 Thesystemengineeringprocess Usuallyfollowsa waterfall modelbecauseoftheneedforparalleldevelopmentofdifferentpartsofthesystemLittlescopeforiterationbetweenphasesbecausehardwarechangesareveryexpensive Softwaremayhavetocompensatefor补偿hardwareproblems Inevitably不可避免involvesengineersfromdifferentdisciplines学科whomustworktogetherMuchscopeformisunderstandinghere Differentdisciplinesuseadifferentvocabularyandmuchnegotiationisrequired Engineersmayhavepersonalagendastofulfil Thesystemsengineeringprocess Inter disciplinary各学科involvement 2 2 1Systemrequirementsdefinition ThreetypesofrequirementdefinedatthisstageAbstractfunctionalrequirements Systemfunctionsaredefinedinanabstractway Systemproperties Non functionalrequirementsforthesystemingeneralaredefined Undesirablecharacteristics Unacceptablesystembehaviourisspecified Shouldalsodefineoverallorganisationalobjectivesforthesystem Systemrequirementsproblems Mustanticipatehardware communicationsdevelopmentsoverthelifetimeofthesystem Hardtodefinenon functionalrequirements particularly withoutknowingthecomponentstructureofthesystem 2 2 2Thesystemdesignprocess Partitionrequirements分割需求Organiserequirementsintorelatedgroups Identifysub systemsIdentifyasetofsub systemswhichcollectivelycanmeetthesystemrequirements Assignrequirementstosub systemsCausesparticularproblemswhenCOTSareintegrated Specifysub systemfunctionality Definesub systeminterfacesCriticalactivityforparallelsub systemdevelopment Thesystemdesignprocess Systemdesignproblems Requirementspartitioningtohardware softwareandhumancomponentsmayinvolvealotofnegotiation商议 Difficultdesignproblemsareoftenassumedtobereadilysolvedusingsoftware Hardwareplatformsmaybeinappropriatefor不相称softwarerequirementssosoftwaremustcompensatefor补偿this Requirementsanddesign Requirementsengineeringandsystemdesignareinextricablylinked Constraintsposedbythesystem senvironmentandothersystemslimitdesignchoicessotheactualdesigntobeusedmaybearequirement Initialdesignmaybenecessarytostructuretherequirements Asyoudodesign youlearnmoreabouttherequirements Spiralmodelofrequirements design 2 2 3Systemmodelling Anarchitecturalmodel体系结构模型presentsanabstractviewofthesub systemsmakingupasystemMayincludemajorinformationflowsbetweensub systemsUsuallypresentedasablockdiagram方块图Mayidentifydifferenttypesoffunctionalcomponentinthemodel Burglaralarmsystem防盗警报系统 Sub systemdescription ATCsystemarchitecture 2 2 4Sub systemdevelopment Typicallyparallelprojectsdevelopingthehardware softwareandcommunications MayinvolvesomeCOTS CommercialOff the Shelf systemsprocurement Lackofcommunicationacrossimplementationteams Bureaucratic官僚andslowmechanism机构forproposingsystemchangesmeansthatthedevelopmentschedulemaybeextended延期becauseoftheneedforrework重做 Theprocessofputtinghardware softwareandpeopletogethertomakeasystem Shouldbetackled解决incrementallysothatsub systemsareintegratedoneatatime Interfaceproblemsbetweensub systemsareusuallyfoundatthisstage Maybeproblemswithuncoordinateddeliveriesofsystemcomponents 对于基于COTS的系统的集成 2 2 5Systemintegration Aftercompletion thesystemhastobeinstalledinthecustomer senvironmentEnvironmentalassumptionsmaybeincorrect Maybehumanresistance抵制totheintroductionofanewsystem Systemmayhavetocoexistwithalternativesystemsforsometime Maybephysicalinstallationproblems e g cablingproblems Operatortraininghastobeidentified 2 2 6Systeminstallation 2 2 7Systemevolution Largesystemshavealonglifetime Theymustevolvetomeetchangingrequirements Evolutionisinherently固有地costlyChangesmustbeanalysedfromatechnicalandbusinessperspective Sub systemsinteractsounanticipatedproblemscanarise Thereisrarelyarationalefororiginaldesigndecisions Systemstructureiscorruptedaschangesaremadetoit Existingsystemswhichmustbemaintainedaresometimescalledlegacysystems 2 2 8Systemdecommissioning退役 Takingthesystemoutofserviceafteritsusefullifetime Mayrequireremovalofmaterials e g dangerouschemicals whichpollutetheenvironmentShouldbeplannedforinthesystemdesignbyencapsulation Mayrequiredatatoberestructuredandconvertedtobeusedinsomeothersystem 2 3Organisations机构 people systems Socio technicalsystemsareorganisationalsystemsintendedtohelpdeliversomeorganisationalorbusinessgoal Ifyoudonotunderstandtheorganisationalenvironmentwhereasystemisused thesystemislesslikelytomeettherealneedsofthebusinessanditsusers Humanandorganisationalfactors Processchanges流程变更Doesthesystemrequirechangestotheworkprocessesintheenvironment Jobchanges工作变更Doesthesystemde skilltheusersinanenvironmentorcausethemtochangethewaytheywork Organisationalchanges机构变更Doesthesystemchangethepoliticalpower权利结构structureinanorganisation Organisational机构processes Theprocessesofsystemsengineeringoverlapandinteractwithorganisationalprocurementprocesses 系统开发过程 采购过程 运行过程Operationalprocessesaretheprocessesinvolvedinusingthesystemforitsintendedpurpose Fornewsystems thesehavetobedefinedaspartofthesystemdesign Operationalprocessesshouldbedesignedtobeflexibleandshouldnotforceoperationstobedoneinaparticularway Itisimportantthathumanoperatorscanusetheirinitiativeifproblemsarise Procurement developmentprocesses Systemprocurement采购 AcquiringasystemforanorganizationtomeetsomeneedSomesystemspecificationandarchitecturaldesignisusuallynecessarybeforeprocurementYouneedaspecificationtoletacontractforsystemdevelopmentThespecificationmayallowyoutobuyacommercialoff the shelf COTS system AlmostalwayscheaperthandevelopingasystemfromscratchLargecomplexsystemsusuallyconsistofamixofofftheshelfandspeciallydesignedcomponents Theprocurementprocessesforthesedifferenttypesofcomponentareusuallydifferent Thesystemprocurementprocess Procurementissues Requirementsmayhavetobemodifiedtomatch匹配thecapabilitiesofoff the shelfcomponents Therequirementsspecificationmaybepartofthecontractforthedevelopmentofthesystem Thereisusuallyacontractnegotiationperiodtoagreechangesafterthecontractortobuildasystemhasbeenselected Contractorsandsub contractors Theprocurementoflargehardware softwaresystemsisusuallybasedaroundsomeprincipalcontractor Sub contractsareissuedtoothersupplierstosupplypartsofthesystem Customerliaseswiththeprincipalcontractoranddoesnotdealdirectlywithsub contractors Contractor Sub contractormodel 2 4Legacysystems遗留系统 Socio technicalsystemsthathavebeendevelopedusingoldorobsoletetechnology CrucialtotheoperationofabusinessanditisoftentooriskytodiscardthesesystemsBankcustomeraccountingsystem Aircraftmaintenancesystem Legacysystemsconstrainnewbusinessprocessesandconsumeahighproportiono