文献翻译——Simulink模型与基于模型的构件集成软件

苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第1页外文文献资料IntegrationofSimulinkModelswithComponent-basedSoftwareModelsAbstractModelbaseddevelopmentaimstofacilitatethedevelopmentofembeddedcontrolsystemsbyemphasizingtheseparationofthedesignlevelfromtheimplementationlevel.Modelbaseddesigninvolvestheuseofmultiplemodelsthatrepresentdifferentviewsofasystem,havingdifferentsemanticsofabstractsystemdescriptions.Usually,inmechatronicssystems,designproceedsbyiteratingmodelconstruction,modelanalysis,andmodeltransformation.ConstructingaMATLAB/Simulinkmodel,aplantandcontrollerbehaviorissimulatedusinggraphicalblockstorepresentmathematicalandlogicalconstructsandprocessflow,thensoftwarecodeisgenerated.ASimulinkmodelisarepresentationofthedesignorimplementationofaphysicalsystemthatsatisfiesasetofrequirements.Asoftwarecomponent-basedsystemaimstoorganizesystemarchitectureandbehaviourasameansofcomputation,communicationandconstraints,usingcomputationalblocksandaggregatesforbothdiscreteandcontinuousbehaviour,differentinterconnectionandexecutiondisciplinesforevent-basedandtime-basedcontrollers,andsoon,toencompassthedemandstomorefunctionality,atevenlowerprices,andwithoppositeconstraints.COMDES(Component-basedDesignofSoftwareforDistributedEmbeddedSystems)issuchacomponent-basedsystemframeworkdevelopedbythesoftwareengineeringgroupofMadsClausenInstituteforProductInnovation(MCI),UniversityofSouthernDenmark.Oncespecified,thesoftwaremodelhastobeanalyzed.OnewayofdoingthatistointegrateinwrapperfilesthemodelbackintoSimulinkS-functions,anduseitsextensivesimulationfeatures,thusallowinganearlyexplorationofthepossibledesignchoicesovermultipledisciplines.苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第2页ThepaperdescribesasafetranslationofarestrictedsetofMATLAB/SimulinkblockstoCOMDESsoftwarecomponents,bothforcontinuousanddiscretebehaviour,andthetransformationofthesoftwaresystemintotheS-functions.Thegeneralaimofthisworkistheimprovementofmultidisciplinarydevelopmentofembeddedsystemswiththefocusontherelationbetweencontrolengineeringandsoftwareengineering.IndexTermscomponent-baseddesign,model-baseddesign,MATLAB/Simulink,modeltransformation,discrete-timemodels,continuous-timemodels.1.INTRODUCTIONSIMULINKisadesign-basedmodelingtool,evenaframework,createdbyMathWorks,thatusesgraphicalblockstorepresentmathematicalandlogicalconstructsandprocessflow,forthemodelling,simulationandanalysisofdynamicsystems.Tothecontrolsystemengineersthestructureandcontentofthesystemrepresentationin.Simulinkisintrinsicandintuitiveandthedesigncanbelayereddependingontheanalysislevelrequired.Simulinkisablockdiagramindustryorientedstandardtoolforsimulatingmixedreactive/transformative,nonlineardynamicsystemsthatbuildsontheMATLABenvironmentfortechnicalcomputing.ASimulinkmodelisarepresentationofthedesignorimplementationofasystemthatsatisfiesasetofrequirements.FormanyyearsSimulinkhasbeenthetoolofchoiceformuchofthecontrolindustry,bymanyconsideredade-factostandard,todevelopbothphysicalandcontrolsystemmodels,intermsofstability,responsetime,overshoot,etc,andismaturingintothenewgenerationofsystemsengineering,representativeofanadvancedapproachtodesign.ThemainattractionofSimulinkhasbeenitsflexibilityandtherangeoftoolboxesavailabletoaidcontrolsystemdesign,developmentandcalibration.COMDES(asafamilyofversions)isacomponent-basedframeworkintendedfordesignandanalysisofembeddedcontrolsystems.SpecificforCOMDESis苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第3页thedesignofthecontrolsystemfromprefabricatedcomponents,andthenanalyzingtheexecutablemodelsthatconstituteitsconfigurationspecification.COMDESoffersstrongtyping,explicitinitialization,explicittimemanagement(delays,clocks,etc),andsimpleexpressionofconcurrency(datadependencies),basedonawell-definedcontrolanddataflowrepresentation.Bymeansofagraphicalsignalflowgrapheditor,itsupportsmodel-baseddevelopment.Theendresultisanintegratedprocessofsoftwaredevelopment,featuringmodel-basedconfigurationandanalysisofembeddedapplicationsthatcanbecharacterizedbythesentence:Whatyouspecifyiswhatyouverify,executeandtest.COMDES(asinitslastversionCOMDES-II)usesanactordiagramthatrepresentssubsystems(actors)andthesignalsexchangedbetweenthemwithinthecorrespondingdistributedtransaction.Anactorencapsulatesstateandexhibitsbehaviour.Individualactorbehaviourisdescribedbymeansofreactivebehaviour,whichisusuallyspecifiedwithastate-machinemodel,andcontinuousbehaviour,i.e.somenumerical(conditioned)processing,thatisspecifiedasafunctionblockdiagram.Theatomicsoftwareunitisafunctionblock.Functionblocksarereusablesystemcomponents,whicheventuallyenablethereconfigurationofsystemstructure.Ultimately,thesystemactordiagramistransformedintoafunctionblockdesignforcontrolanddata.Althoughthedifferentdisciplinesaretightlycoupledintheconsideredembeddedsystems,theirdevelopmentisoftenarathersequential,mono-disciplinary,process.Typically,firstthecontrolpartisdesigned,nextthehardwareinfrastructureisfixed,andfinallytheembeddedsoftwareisdeveloped.Thisapproachcancreatelargeproblems,especiallyforthesoftwareengineers.Forinstance,choicesabouttheplacementsofsensors(andimplicitlytheoccurrenceofinterrupts),controlrates,controldelays,hardware,etc.,haveastronginfluenceonthecomplexityofthesoftware.Moreover,usuallymanyimplicitassumptionsaremade,whichfirstbecomevisibleatsystemintegration.Thiseasilyleadstonon-optimalsolutions.苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第4页Withineachdiscipline,acommonsolutionisthefrequentuseofmodelstodetectproblemsasearlyaspossible.Usingthemodel-basedengineeringparadigmforthedesignofasystem,themodelsarepreferablyspecifiedusingdomainspecificmodellingformalisms.Forinstance,inthesoftwaredomainalotofeffortisputonmodeldrivendevelopment,basedoncomponentmodels.Moreover,mono-disciplinarymodelingisusuallysupportedbytoolsthatallowsomeformofexecutionorsimulation.Lacking,however,isthepossibilitytocombinetoolsofdifferentdisciplines,toinvestigatethemutualinfluenceofmodelingchoices.OuraimistocouplecurrentlyusedtoolstoallowbothautomatictranslationoftheSimulinkmodelstoCOMDEScomponentbasedmodels,butalsosimulationofthetransformedsoftwaremodelsintotheSimulinksetup.Bymeansofco-simulation,thecomponentmodelscanbecombinedtoobtainabetteroverallsystembehavior.2.MODEL-BASEDDESIGNINCONTROLANDSOFTWAREModel-baseddesignprovidesaproventechniqueforcreatingembeddedcontrolsystems.Model-basedsystemdevelopmentisachangeoffocusfromarithmeticanddatarelatedissuestotheoverallarchitectureofsoftwaresystem.Itisamoreeffectiveapproachtoincreasesystemfunctionalityandreliability,andtodecreasedevelopmentcostandtime.Thedesignofcontrolalgorithmsisafundamentalpartofthedesignflow.Itstartsfromafunctionalspecificationandendsupwithadetaileddescriptionofthealgorithms.Inthemodel-baseddesignmethodology,thepartofthecontrolalgorithmthatismappedtothesoftwarepartitionisautomaticallytranslatedfromamodelrepresentationtoasetofsoftwarecomponents.Thesoftwarearchitectureoftheapplicationwillaccommodateandcomposetogetherthosesoftwarecomponentssuchthatthereal-timerequirementsaremet.Intheproposeddesignflow,thecontrolalgorithmsarecapturedusingtheMATLAB/SimulinkdesignenvironmentandtheautomatictranslationofthemodeltoCOMDES-languagecodeisperformedaccordingtoasetofrules,describedinafollowingsection.苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第5页Thesystemcanthenbespecifiedasintheformabove,wherethevectorugivestheinputsignalstothesystem,ygivesthevectorofoutputsignalsfromthesystemandthevectorxgivesthestateofthesystem.ASimulinkmodelisrepresentedgraphicallybymeansofanumberofinterconnectedblocks.Linesbetweenblocksconnectblockoutputstoblockinputsandrepresentdataflowsignals.Blocksmayhavestates,whichmayconsistofadiscrete-timeandacontinuous-timepart.Theoutputofablockiscomputedbyanoutputfunction,basedonitsinputanditscurrentstateandtime.Similarly,anupdatefunctioncalculatesthenextdiscretestate.Aderivativefunctionrelatesthederivativesofthecontinuouspartofthestatetotimeandthecurrentvaluesoftheinputsandthestate.Blockscanbebuiltfromalargenumberofpredefinedlibraryblocks,whichcanbenestedinanarbitrarystructurecontainercomposition,ortheycanbeimplementedbyanSfunction,whichcanbewritteninMATLAB,C,C+,Ada,orFortran,belongingtoSimulinkscallbackarchitecture.AnS-functioncanbeusedforavarietyofapplicationssuchasdescribingasystemasasetofmathematicalequations,incorporatingexistingcodeintoasimulation,andaddingablockthatrepresentatheschedulerofareal-timekernel.DuringthesimulationofaSimulinkmodel,theoutputs,inputsandstatesarecomputedatcertainintervals,fromastarttimetoanendtime,asspecifiedbytheuser.Thesuccessivestatesofasystemarecomputedbyaso-calledsolver,aSimulink-specificprogram.Sincenosolverissuitableforallmodels,thereareseveraltypesofsolvers.Thesolversusenumericalintegrationtocomputethecontinuousstatesofasystemfromthestatederivativesspecifiedbythemodel.Eachsolverusesadifferentintegrationmethod,allowingtheselectionofthemostsuitablemethodforaparticularmodel.Thesuccessivetimepointsatwhichthestatesandoutputsarecomputed苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第6页arecalledtimesteps.Thelengthoftimebetweenstepsiscalledstepsize.Thestepsizedependsonthetypeofthesolverused,thecharacteristicsoftheSimulinkmodel,andtheexistenceofdiscontinuitiesofthecontinuousstates(Simulinkchecksforsuchdiscontinuitiesthisiscalledzerocrossingdetectionandifitdetectsonewithinthecurrentstep,theprecisetimeatwhichzerocrossingoccursisdeterminedandadditionaltimestepsaretaken).SimulationofaSimulinkmodelstartswiththeinitializationphase,wheree.g.libraryblocksareincorporated,blockparametersareevaluated,memoryisallocatedandtheexecutionorderoftheblocksisdetermined.Next,Simulinkentersasimulationloop,consistingofsimulationsteps.Duringeachsimulationstep,Simulinkexecutesallblocksofthemodelintheorderdeterminedduringinitialization.Thisexecutionorderdoesnotchangeduringthesimulation.Foreachblock,Simulinkcallsfunctionsthatcomputetheblocksstates,derivatives,outputsforthecurrentsampletime,andthenexttimestep.Thiscontinuesuntilthesimulationiscomplete.COMDESwhichisbeingdevelopedatMCI,UniversityofSouthernDenmark,isaninstanceofcomponentbaseddesign,whichisasoftwaredesignmethodforreal-timeembeddedsystems.COMDESisanexecutablevisualmodelforembeddedcontrolsystems.Itmirrorsthearchitectureofthecontrolprocessitself,whichismadeupofanumberofindependentcontrolmodules,calledfunctionblocks,withatop-levelmodulecontroller,wiredbysignals,suchaspressure,temperature,etc.TheCOMDESsystemdesignismeanttobeadiagramofcomponentstogetherwithadescriptionoftheirinterconnectiontopologyand/orstatebasedbehavior.Thenativetimingexecutionofthemodelisaperiodicallyclockedeventspattern(underamoregeneralparadigmcalledtimedmultitasking).3.TRANSLATIONOFSIMULINKMODELSTOCOMDESMODELSOurapproachtotranslatebottom-upandhierarchicalthecontrollerpartoftheSimulinkdesign,coveringfunctionalandtimingaspects,isbasedon:苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第7页mappingtablesbetweenasafesetofSimulinkblocksandthecorrespondingCOMDESfunctionblockmodel.asetoftranslationrulesformulatedforbothStateflowandSimulinkconditionalblocksforconvertingofsomeimplicitlybehaviourintoanexplicitlyone:deriveCOMDESstatemachinemodeloutoftheStateflowstatemachine,associatedinputandoutputvariablesandconditionalblockslikeSwitch,Multiportswitch,andassociatethecontinuouspartofSimulinktothestatesoftheCOMDESstatemachinemodelintermsofthefunctionblocks(basicandcomposite,respectively).mappingoftypesandtimingconstraintstranslationoftheSimulinkdesignintotheCOMDESsoftwaredesignusinganintermediateXML-basedmodel,whichrepresentsaCOMDESmodelintermsofclass,attributes,andnode-basedhierarchies,accordingtotherulesestablishedintheprevioussteps.4.INTEGRATIONOFTHECOMDESBLOCKSINTOS-FUNCTIONSInorderforthesimulationtocaptureaccuratebehaviorofthesubsystemsoftwareinrealtime,itisessentialthatthesamesoftwaretobemodeledinthesimulationsetupaswell.SimulinkusesblockdiagramstomodeldynamicsystemsandprovidesanenvironmentthatallowssimulationofCOMDEScomponent-basedmodelsbyconvertingofsoftwarecomponentsintocustomS-functions.SimulinkprovidesthenecessarytemplatestocreateanS-function,andthesoftwaremodelswillbeexecutedwithintheSimulinkshellasS-functions,Figure1.苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第8页Figure1.EncapsulationofaCOMDEScontrollerintoaSimulinkSfunction.ControlengineerscansimulateandthusverifytheCOMDEScomponent-basedmodelimplementationbycomparingitsperformancetothatofpureSIMULINKmodelsofthecontroller,andthiscanhappeniteratively,allowinganearlyevaluationofthedevelopmentprocess.AnS-functionisasystemfunctionthathasbeencompiledtorunintheSimulinkenvironment.OnaMicrosoftWindowsplatform,thesesystemfunctionsarecompiledintodynamicallylinkedlibraries(DLLs).ThesoftwarecomponentisthencompiledandbuiltusingtheMATLABmexfunctionlibrary.ThisbuildprocesswithintheMATLABapplicationproducesaDLLforthesoftwarecomponent.TheMATLAB-producedDLListhenusedinthesimulationmodelbyassociatingitwithauserdefinedSfunction.Thiswillallowtoaccuratelysimulateseveralmodesofoperationandtoimprovethecontrolalgorithmsintherealapplication,oncethesimulationresultsmettheirtargets.AnS-functionimplementasetofmethods,calledcallbackmethodsthattogetherdescribethebehaviorofthe(sub)systemmodelledbymeansoftheS-function.Thesimulationcoordinator,inourcaseMatlabSimulink,invokesthesecallbackmethodsduringthesimulation.AnimplementationoftheS-functioninterfacemustimplementthesetofcallbackmethods.Somecallbackmethodsareoptional.Inthisway,thesimulationcoordinatorcancomputethestatesfortheS-function.IftheS-functioncontainsnonsampledzerocrossings,thesimulationcoordinatorcallstheoutputandzero-crossingsportionsoftheS-苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第9页functionatminortimestepssothatthezerocrossingscanbelocated.5.CONCLUSIONInthispaperweproposedamethodologyoftransformingSimulinkcontrolmodelsintoCOMDESsoftwarecomponent-basedmodels.Model-baseddesign,usedtoitsfullest,providestranslation-connecteddesignenvironmentsthatenabledeveloperstouseSimulinkasasinglemodeloftheirentiresystemforvisualizationandvalidation,andultimatelysoftwareproductdeployment,withconsistentautomaticcodegeneration.Inthisrespect,someproblemissuesmaybesolvedbyajointcontrolengineerandsoftwareengineereffort.Evenifthecontrolandsoftwaredesignworkisdoneinisolation,thereisaclosecooperationbetweenthetwoexpertises.Thecontrolengineerscanconcentrateontheirspecificissues,likedamping,overshoots,stabilityofcontrol,whereasthesoftwareengineerscanfocusonembeddedaspectslikeschedulingissues,resourceconsumption,priorities.Theinteractionisdirectlybetweenthetwomodels,liketherelationbetweenthecontrolloopexecutionperiodsandthetaskdeadlines.TheadvantagesofusingCOMDESasasoftwaredesignandimplementationmethodofSimulinkcontrolmodelsarethestraightforwardofthetranslation,wellstructureddesign,feasibilityofverificationandvalidationbycombiningdifferenttechniques,reusabilityofpartsoftheseinrelationtoreuseofcomponents,andcost-efficientdevelopmentofcode.WeintendtoimprovethetranslationtohandleotherSimulinksemantics.Themodel-baseddevelopmentprocessbenefitsfromcontrol-softwareco-design,resultingfasterandshorterdevelopmentcyclesandearliertesting.Maintenanceofthecontrolalgorithmsbecomeseasybecausecontrolalgorithmmodelsaresafelytranslatedintocomponent-basedsoftwarearchitectures,andwrappingbacksoftwarecomponentsintoalibraryofsimulationcomponents,Simulinkisusedasatestingtooltoo.Inthisway,asimulationtool苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第10页independentrepresentationofthecontrolalgorithmshasbeenachieved.Thenewopportunitiesforcheckingandthecleardivisionbetweencontrolalgorithmandsimulationcodehasbeenappreciated.苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第11页中文翻译稿Simulink模型与基于模型的构件集成软件摘要基于发展旨在通过强调从执行层面设计水平的分离，便于嵌入式控制系统的开发模型。基于模型的设计涉及到多种模型的应用，它们代表一个系统的不同的视角，这个系统有对抽象系统描述的不同的词义。通常，在机电一体化系统的设计过程，通过迭代模型的构建，分析模型，模型转换来推进设计进程。构建一个MATLAB/Simulink模型，通过使用图形块来表示数学和逻辑结构和工艺流程来模拟植物和控制器的行为，然后软件代码生成了。仿真模型是一个满足一组要求的物理系统的设计和实现的代表。一个软件组件的系统的目的是组织系统的结构和行为作为计算的一种手段，通信和约束条件，利用计算模块和集料的离散和连续的行为，基于时基控制器事件不同的互连和执行纪律，等等，包括要求更多的功能，甚至更低的价格，并与相反的约束。COMDES是一个基于组件的系统框架由南丹麦大学的克劳森产品创新研究所开发的软件工程组。一旦被指定，该软件模型需要进行分析。这样做的一个方法是集成在封装文件的模型到SimulinkS函数，并利用其广泛的模拟功能，从而允许在多学科设计选择的可能的早期探索。本论文介绍了一种安全的一个限定的MATLAB/Simulink块COMDES软件组件的翻译，无论是连续和离散行为，并讲软件系统转化为S函数。这项工作的总体目标是通过重视控制工程和软件工程之间的关系来提高嵌入式系统的多学科发展。索引条款-基于组件的设计，基于模型的设计，MATLAB/Simulink，模型转换，离散模型，连续时间模型1.介绍Simulink是基于设计的建模工具，甚至是一个框架，由Mathworks创造，使用图形块表示的数学和逻辑结构和流程，为动态系统建模，仿真与分析。对系统的描述控制系统工程师的结构和内容。Simulink是内在的、直观的，同时设计可以根据分析所需的水平进行分层。Simulink是一种面向框图工业模拟混合反应/转换标准的工具，基于MATLAB环境的苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第12页计算技术的非线性动态系统。仿真模型是一个能够满足一系列要求的设计或执行代表。多年来，Simulink的已成为很多控制行业进行选择的工具，被许多人认为是事实上的标准，在稳定性，响应时间，过冲，等方面同时发展了物理和控制系统模型2，6，并正在成熟为新一代的系统工程，是一种先进的设计方法的代表。Simulink的主要吸引力是它的灵活性和可用的辅助控制系统设计，开发和校准的工具。COMDES是一个基于组件的框架用于嵌入式控制系统的设计与分析。具体的COMDES是由预制组件构成的控制系统的设计，然后分析对构成其配置规范的可执行模型进行分析。COMDES提供强大输入，显式初始化，显式时间管理（延迟，时钟，等），和并发的基于一个明确的控制和数据流的简单表达方式（数据依赖关系）。通过图形信号流图编辑工具，它支持基于模型的开发。最终的结果是一个集成的软件开发过程，基于模型的配置和分析嵌入式应用程序的特征可以用一句来说明：你指定的是什么，你验证指定，执行和测试的就是什么。COMDES（如其后的版本comdes-ii）使用一个执行图表示的子系统和它们之间在相应的分布式事务中的信号交换。一个执行器封装状态和表现出其动作。个体执行器行为由一系列反应行为描述，这通常以一个状态机模型和连续的动作为特征，即：一些数值（条件）处理，被指定为一个功能块图。原子级的软件单元是一个功能块。功能块是可重复使用的系统组件，最终使系统结构能够重构。最终，系统执行图被转化为控制和数据功能块设计的功能模块。尽管不同学科紧密耦合在所考虑的嵌入式系统中，他们的发展往往是相当的有顺序，单学科进行，有一定过程。通常，首先设计控制部分，然后硬件设施被确定下来，最后的嵌入式软件被开发出来。这种方法可以创造大量的问题，尤其是对于软件工程师来说。例如，传感器的位置的选择（和隐式地发生中断），控制率，控制延迟，硬件，等，它们对软件的复杂性有着很大影响。此外，通常很多隐含的假设被提出，它首先成为可见的系统集成。这很容易导致非最优解。在每一个学科中，频繁地使用模型来及早发现问题是一种常见的解决方案。使用基于模型的工程范例系统的设计模型，最好是指定使用具体域建模形式主义。例如，软件领域中很多的精力被放在基于组件模型的模型驱动的开发。此外，单一学科建模通常由允许某种形式的执行或仿真的工具来支持。但是，缺乏是可能结合不同学科的工具，调查建模选择的相互影响。我们的目标是对目前使用的工具进行配对，以同时允许Simulink模型向COMDES基于构件模型的自动转换，同时将仿真软件Simulink模型转化苏州大学本科生毕业设计（论文）附件：外文文献资料与中文翻译稿第13页为Simulink设置。通过联合仿真方法，组件模型可以被组合以获得更好的整体系统的行为。2.基于模型控制和软件的设计基于模型的设计提供了用于创建嵌入式控制系统的一种行之有效的方法。基于系统开发的模型是一个变化的算法和数据系统的软件总体结构相关的问题。这是增加系统的功能和可靠性的一个更有效的方法，同时能减少开发成本和时间。控制算法的设计是设计流程中的一个基本组成部分。它从功能规格开始，以算法的详细描述结束。在基于模型的设计方法中，该映射到分区的软件控制算法的一部分自动从模型表示翻译成一组软件组件。应用程序的软件体系结构将容纳和组合到一起的那些软件组件，满足实时性的要求。在所提出的设计流程，控制算法，使用MATLAB/Simulink环境设计和自动翻译COMDES语言代码的模型是根据一组规则捕获的，这在下面的部分描述。本系统可以为上述规定，其中向量u给系统输入信号，y给出了从系统输出信号,变量量X给出了系统的状态。一个Simulink模型是由若干相互连接的块表示的图标表示。块之间的连线使块的输入和输出相连，它们表示数据流信号。块可能有的状态，这可能包括一个离散时间和连续时间部分。一个块的输出通过输出函数计算，根据其输入和它的当前状态和时间。同样，一个更新函数计算下一个离散状态。衍生功能使连续部分的衍生物对时间的输入和状态的当前值相联系。块可以由大量预定义的库模块构建，它们可以嵌套在任意结构的容器中，也可以由一个S函数