軟件體系結構—調用/返回風格軟件體系結構課程組本節(jié)內容調用/返回風格1風格變種22課程總結3調用/返回風格主程序/子程序風格經(jīng)典的編程范式：功能分解面向對象/抽象數(shù)據(jù)類型（ADT）信息(表示,方法方法)隱藏層次結構每一層只能與其直接相鄰的鄰居進行通信其他客戶端/服務器……調用/返回風格主程序/子程序風格單線程控制，劃分為若干處理步驟功能模塊：把步驟集成至模塊中抽象數(shù)據(jù)類型（ADT）操作和數(shù)據(jù)綁定在一起，隱藏實現(xiàn)和其他秘密面向對象方法（動態(tài)綁定），多態(tài)（子類），重用（繼承）對象活動于不同的進程/線程（分布式對象）CS結構、分層風格組件多個接口，二進制兼容，高級中間件主程序/子程序風格主程序/子程序風格Problem:Thispatternissuitableforapplicationsinwhichthecomputationcanappropriatelybedefinedviaahierarchyofproceduredefinitions.Context:Manyprogramminglanguagesprovidenaturalsupportfordefiningnestedcollectionsofproceduresandforcallingthemhierarchically.Theselanguagesoftenallowcollectionsofprocedurestobegroupedintomodules,therebyintroducingname-spacelocality.Theexecutionenvironmentusuallyprovidesasinglethreadofcontrolinasinglenamespace.Solution:Systemmodel:callanddefinitionhierarchy,subsystemsoftendefinedviamodularityComponents:proceduresandexplicitlyvisibledataConnectors:procedurecallsandexplicitdatasharingControlstructure:singlethread模塊分解ParnasHidesecrets.OK,what’sa“secret”?RepresentationofdataPropertiesofadevice,otherthanrequiredpropertiesMechanismsthatsupportpoliciesTrytolocalizefuturechangeHidesystemdetailslikelytochangeindependentlyExposeininterfacesassumptionsunlikelytochangeUsefunctionstoallowforchangeThey’reeasiertochangethanvisiblerepresentation封裝/信息隱藏Parnas:Hidesecrets(notjustrepresentations)Booch:Object’sbehaviorischaracterizedbyactionsthat

itsuffersandthatitrequiresPracticallyspeaking:Objecthasstateandoperations,butalsohasresponsibilityfortheintegrityofitsstateObjectisknownbyitsinterfaceObjectisprobablyinstantiatedfromatemplateObjecthasoperationstoaccessandalterstateandperhapsgeneratorTherearedifferentkindsofobjects(e.g.,actor,agent,server)數(shù)據(jù)抽象/面向對象數(shù)據(jù)抽象/面向對象Problem:Thispatternissuitableforapplicationsinwhichacentralissueisidentifyingandprotectingrelatedbodiesofinformation,especiallyrepresentationinformation.Context:Numerousdesignmethodsprovidestrategiesforidentifyingnaturalobjects.Newerprogramminglanguagessupportvariousvariationsonthetheme,soifthelanguagechoiceorthemethodologyisfixed,thatwillstronglyinfluencetheflavorofthedecomposition.Solution:Systemmodel:localizedstatemaintenanceComponents:managers(e.g.,servers,objects,abstractdatatypes)Connectors:procedurecallControlstructure:decentralized,usuallysinglethread面向對象體系結構的元素Encapsulation:Restrictaccesstocertaininformation

封裝：限制對某些信息的訪問Interaction:Viaprocedurecallsorsimilarprotocol

交互：通過過程調用或類似的協(xié)議Polymorphism:Choosethemethodatrun-time

多態(tài)：在運行時選擇具體的操作Inheritance:Shareddefinitionsoffunctionality

繼承：對共享的功能保持唯一的接口Reuseandmaintenance:Exploitencapsulationandlocalitytoincreaseproductivity

復用和維護：利用封裝和聚合提高生產(chǎn)力面向對象方法的問題ManagingmanyobjectsVastseaofobjectsrequiresadditionalstructuring

對象的海洋需要額外的結構來容納HierarchicaldesignsuggestedbyBoochandParnasManagingmanyinteractionsSingleinterfacecanbelimiting&unwieldy(hence,“friends”)

單一的接口能力有限并且笨拙（于是，”友元”）Somelanguages/systemspermitmultipleinterfaces(innerclass,interface,multipleinheritance)DistributedresponsibilityforbehaviorMakessystemhardtounderstandInteractiondiagramsnowusedindesignCapturingfamiliesofrelateddesignsTypes/classesareoftennotenoughDesignpatternsasanemergingoff-shoot如何管理大的對象數(shù)據(jù)集PureO-OdesignleadstolargeflatsystemswithmanyobjectsSameoldproblemscanreappearHundredsofmodules=>hardtofindthingsNeedawaytoimposestructureNeedadditionalstructureanddisciplineStructuringoptionsLayers(whicharenotnecessarilyobjects)SupplementalindexHierarchicaldecomposition:bigobjectsandlittleobjects體系結構風格變種Client-serverObjectsareprocesses

進程就是對象Asymmetric:clientknowsaboutservers,butnotviceversa

不對稱：客戶端知道服務器，反之則不然TieredElaborationonclient-server

C/S模式的擴展Aggregationintorun-timestrata

運行時層的結合Usuallysmallnumberoftiers

通常只有少量的層Components(later)MultipleinterfacesSpecialprotocolsfordynamicreconfiguration

支持動態(tài)配置的專門協(xié)議層次風格案例-操作系統(tǒng)硬件OS應用應用應用平臺層次案例-計算機網(wǎng)絡層次風格Problem:Thispatternissuitableforapplicationsthatinvolvedistinctclassesofservicesthatcanbearrangedhierarchically.Oftentherearelayersforbasicsystem-levelservices,forutilitiesappropriatetomanyapplications,andforspecifictasksoftheapplication.Context:Frequently,eachclassofserviceisassignedtoalayerandseveraldifferentpatternsareusedtorefinethevariouslayers.Layersaremostoftenusedatthehigherlevelsofdesign,usingdifferentpatternstorefinethelayers.Solution:Systemmodel:hierarchyofopaquelayersComponents:usuallycomposites;compositesaremostoftencollectionsofproceduresConnectors:dependsonstructureofcomponents;oftenprocedurecallsunderrestrictedvisibility,mightalsobeclient/serverControlstructure:singlethread層次風格參考結構層次風格特點每層為上一層提供服務，使用下一層的服務，只能見到與自己鄰接的層適當時候(必不得已的時候)，可以允許一定的越層操作大的問題分解為若干個漸進的小問題，逐步解決，隱藏了很多復雜度修改一層，最多影響兩層，而通常只能影響上層。接口穩(wěn)固，則誰都不影響上層必須知道下層的身份，不能調整層次之間的順序層層相調，影響性能

服務器客戶客戶客戶客戶客戶LocalLoopback客戶端/服務器風格兩層C/S結構三層C/S結構B/S結構（瀏覽器/服務器風格）客戶端/服務器風格兩層客戶端/服務器風格C/S軟件體系結構是基于資源不對等，且為實現(xiàn)共享而提出的，20世紀90年代成熟起來C/S體系結構有三個主要組成部分：數(shù)據(jù)庫服務器、客戶應用程序和網(wǎng)絡服務器（后臺）負責數(shù)據(jù)管理，客戶機（前臺）完成與用戶的交互任務?！芭挚蛻魴C，瘦服務器”缺點：對客戶端軟硬件配置要求較高，客戶端臃腫客戶端程序設計復雜數(shù)據(jù)安全性不好?？蛻舳顺绦蚩梢灾苯釉L問數(shù)據(jù)庫服務器。信息內容和形式單一用戶界面風格不一，使用繁雜，不利用推廣使用軟件維護與升級困難。每個客戶機上的軟件都需要維護兩層客戶端/服務器風格與二層C