《软件体系结构》课件 05-虚拟机体系结构风格

软件体系结构—虚拟机风格软件体系结构课程组本节内容虚拟机风格1解释器风格22规则引擎34课程总结虚拟机风格Interpreters（解释器）SimulatefunctionalitywhichisnotnativetothehardwareRule-basedsystems（规则系统）SpecializationofaninterpreterOtherSyntacticshellsCommandlanguageprocessors解释器风格Problem:

Thispatternissuitableforapplicationsinwhichthemostappropriatelanguageormachineforexecutingthesolutionisnotdirectlyavailable.Thepatternisalsosuitableforapplicationsinwhichthecoreproblemisdefininganotationforexpressingsolutions,forexampleasscripts.Interpretersaresometimesusedinchains,translatingfromthedesiredlanguage/machinetoanavailablelanguage/machineinaseriesofstages.Context:

Theinterpreterwillmostoftenbedesignedtobridgethegapbetweenthedesiredmachineorlanguageandsome(possiblyvirtual)machineorlanguagealreadysupportedbytheexecutionenvironment.解释器风格Solution:Systemmodel:virtualmachineComponents:onestatemachine(theexecutionengine)andthreememories(currentstateofexecutionengine,programbeinginterpreted,currentstateofprogrambeinginterpreted)Connectors:dataaccessandprocedurecallControlstructure:usuallystate-transitionforexecutionengine;inputdrivenforselectionofwhattointerpretSignificantVariants:Expertsystemsareoftenimplementedasinterpretersforthecollectionsofrules,orproductions,thatrepresenttheexpertise.Becausetheproductionsrequireacomplexselectionrule,specializedformsofinterpretershaveevolved.解释器风格解释器风格：优势Functionality:Cansimulatenon-nativefunctionalityTesting:Cansimulate“disaster”modes(e.g.forsafety-criticalapplications)Flexibility:Verygeneral-purposetool解释器风格：劣势Efficiency:Much,muchslowerthanhardwareMuchslowerthancompiledsystemTesting:Additionallayerofsoftwaretobeverified解释器风格：用途解释型语言VB、Javascript、VBScript、HTML、Java字节码、Matlab脚本、配置文件通信协议用户输入游戏中的组合按键规则系统风格规则系统特征Codetobeexecuted(knowledgebase)Interpretationengine(ruleinterpreter)Controlstateofinterpreter(rule/dataselection)Currentstateofthecode(workingmemory)复杂规则系统示例规则系统的抽象黑板系统与规则系统的相似性一个实际的规则引擎：DroolsDrools是Redhat公司JBoss业务逻辑智能模块/drools/Drools是处理规则的专家系统一个实际的规则引擎：Drools声明式编程规则引擎允许你说“做什么”，而不是“怎样去做”规则系统能解决非常困难的难题逻辑和数据分离快捷和灵活知识集中化工具集成良好的解释机制易于理解的规则一个例子产生背景系统庞大，业务复杂业务规则经常改变24小时服务业务统一管理降低系统维护升级成本产生式规则引擎许多产品规则系统的大脑实际上就是一个推理引擎，用于匹配事实（Fact）和规则（Rule）当匹配被找到，规则对应的动作（Action）会被触发（Fire）动作经常会改变事实的状态，或者在应用上执行一些“外部”动作RETE网络节点简单的RETE网络Drools体系结构Drools体系结构与经典的规则引擎对比虚拟机风格总结Interpreters（解释器）Simulatefunctionalitywhichisnotnativetotheha