軟件開發(fā)設(shè)計外文翻譯文獻本科畢業(yè)論文

軟件開發(fā)設(shè)計外文翻譯文獻本科畢業(yè)論文外文資料原文

SoftwareDevelopmentConceptsandDesign

Methodologies

Duringthe1960s,mainframesandhigherlevelprogramminglanguageswereappliedtomanyproblemsincludinghumanresourcesystems,reservationsystems,andmanufacturingsystems.Computersandsoftwarewereseenasthecureallformanybusinessissuesweresometimesappliedblindly.Systemssometimesfailedtosolvetheproblemforwhichtheyweredesignedformanyreasonsincluding:?Inabilitytosufficientlyunderstandcomplexproblems

?Notsufficientlytakingintoaccountend-userneeds,theorganizationalenvironment,andperformancetradeoffs

?Inabilitytoaccuratelyestimatedevelopmenttimeandoperationalcosts

?Lackofframeworkforconsistentandregularcustomercommunications

Atthistime,theconceptofstructuredprogramming,top-downdesign,stepwiserefinement，andmodularityemerged.Structuredprogrammingisstillthemostdominantapproachtosoftwareengineeringandisstillevolving.Thesefailuresledtotheconceptof"softwareengineering"basedupontheideathatanengineering-likedisciplinecouldbeappliedtosoftwaredesignanddevelopment.

Softwaredesignisaprocesswherethesoftwaredesignerappliestechniquesandprinciplestoproduceaconceptualmodelthatdescribesanddefinesasolutiontoaproblem.Inthebeginning,thisdesignprocesshasnotbeenwellstructuredandthemodeldoesnotalwaysaccuratelyrepresenttheproblemofsoftwaredevelopment.However,

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designmethodologieshavebeenevolvingtoaccommodatechangesintechnologycoupledwithourincreasedunderstandingofdevelopmentprocesses.

Whereasearlydesignmethodsaddressedspecificaspectsofthedevelopmentprocess,currentmethodsattempttoaddresstheentirescopeofsoftwaredevelopment.Softwaredesignmethodsareoftenclassifiedinreferencetotheperiodinwhichtheywereintroducedandtheproblemsatthattime.Drivenbycodingandtestingproblems,toolsandmethodsweredeveloped.Earlymethodsfocusedonmodularityandtop-downdevelopment,andinformationhidingthroughabstraction.Thisledtothedevelopmentofstructuredlanguages,structuredanalysis,anddataflowanalysis.

Inthelastdecadeorso,theexpenseinvolvedinautomationhasshiftedfromhardwaretopeople.Therefore,thesoftwareengineeringcommunityhasbeenfocusedonobjectoriented(O-O)designandtheconceptofre-usablecodeinordertoreducethehumancostcomponent.InefficientdesignsanddevelopmentmethodologieshavebeenaddressedwithComputerAidedSoftwareEngineering(CASE)tools,andfourthgenerationdesignlanguages.Thishasbeendoneinanattemptreplacethetraditionalwaterfalllifecycleprocessmodelunderwhichmostexistingsoftwarehasbeendeveloped.

一、SoftwareDesignFundamentals

Softwaredesignmethodsallaimtoprovidethesoftwaredesignerwithasystemblueprint.Thisblueprintusuallyhasthreeaspects:data,architectural,andprocedural.

?Datadesignreferstothedata'sorganization,relationships,accessandprocessingmethods.

?Architecturaldesigndefinesthecomponentsofthesystemandtheirrelationships.

?Proceduraldesignbuildsonthedataandarchitecturaldesign

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phasestodescribetheprocessingdetailsofthesystem.

Eventhoughtherearenumerousdesignmethodologies,theirbasicconceptsareverysimilar-Allsoftwaredesignmethodspartitiontheproblemandsoftwareintosmallerpiecesinordertoreducecomplexity.Theyallstrivetoidentifydatastructuresandfunctions,andprovidemeasurementsforsoftwarequality.Someofthecommonprinciplesinsoftwaredesigninclude:stepwiserefinement,softwarearchitecture,programstructure,datastructure,softwareprocedures,modularity,

abstraction,andinformationhiding.

二、ModernDesignMethodologies

Conventionalsoftwaredevelopmentpracticescangenerallybemappedontothetraditionallife-cyclephasesofanalysis,

functionalspecification,desi

gn,implementation,testing,and

maintenance.Thisthoughtprocessisinadequatefortoday's

complexinformationsystems.Asthedeman

dforsoftwar

eisgrowingmuchfasterthanthenumbero

fdevelopers,adherin

gtoconventionaltechniquessuc

hasthewaterfallmethodrequirestoomuchtime,toomanypeople,andisdifficulttomanage.Hence,manynewsoftwaredevelopmenttechnologieshavearisen.Newlydevelopedpract

icesandmodelsdonotattempttoseparatephasesofsoftwaredevelopment,suchasspecificationandimplementation,butinsteadfocusontheconceptofprogramtransformationthroughstepwiserefinementanditeration.

1、Object-OrientedTechnology

Object-Oriented(O-O)softwaredesigntechnologyisfundamentallydifferentfromthetraditionalmethodsdescribedabove.Withtraditionalmethods,eachmoduleisrecognizedamajorstepintheoverallprocessandtheprocessgoesfromonesteptothenext.Ontheotherhand,O-Odesignisstructuredaroundamodelofobjectsandthefunctionstheyperform.

O-OprogrammingcanbetracedtothesimulationlanguageSIMULA,a

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highlevellanguagedevelopedinthelate60'sthatintroducedobjectclassesasamethodtoencapsulatedata.Later,inthe1970s,Smalltalkwasintroducedasacompletegrapghdesignandcodingasdetailisaddedtothedesign.Thisprovidesacommonlanguagethroughouteachstageindevelopment.O-OisbestappliedwithspecificallydesignedO-Odevelopmenttools,butitisimportanttorememberthatasamethodologyisitnotspecifictoanyprogramminglanguage.Manydifferentprogramminglanguagescanbeusedtoimplement0-0technologyanddesignmethodologies.

Insteadofproceduresandfunctionspassingdatabackandforth,inobjectorienteddesign,thesystemisviewedasacollectionofobjectswithmessagespassedfromobjecttoobject.Eachobjecthasitsownsetofassociatedoperations.Object-orienteddesignisbasedontheideaofinformationhidingandmodularizationofbothdataandprocessing.Itisbestusedwhenneitherdatastructurenorprocessingoperationsarewelldefinedaheadoftime.Thisisquiteusefulintoday'sbusinessenvironmentwhererequirementsarealwayschangingandnotverywelldefined.Thus,ithasbecomequitepopular!Theconceptofobjectsperformingservicesisanaturalwayofthinkingforbothdevelopersandcustomers.Thisfacilitatesunderstandingtheproblemdomainandamorenaturaldesign.Inaddition,therearemanybenefitsofobject-orienteddevelopment.Theseinclude:

?Inheritancecapitalizesonthecommonaltyofattributesandservicesallowingcodeandobjectstobere-used.

.Informationhidingmakessystemsmorestablebylocalizingchangestoobjectsandtherebymakingthemreusable.

.Theobject-orienteddevelopmentprocessisconsistentfromanalysis,throughdesign,tocoding.

MoreinformationonObjectOrientedProgrammingprinciplescanbefoundinChapter4-OrganizationofProgrammingLanguagesand

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ProgrammingConcepts.

2、Prototyping

Prototypingwasinventedbecauseendusersparticipatinginthedevelopmentphasefounditdifficulttounderstandrequirementspecificationsandconceptualmodels.However,whenitfirstbeganbeingusedinthe1980s,mostconventionallifecycledevelopersconsidereditexpensiveandtimeconsuming.

Sincethattime,usersanddevelopershaveusedprototypessuccessfullyasacommunicationstooltodemonstratesystemrequirements.Afterseveralprototypeiterations,developershaveabetterunderstandingofuserrequirementsandusershaveabetterideaofhowthesystemwilleventuallywork,look,andl.

Thenumberoftimestheprototypeisincrementallyrefineddependsonhowwelltheuserrequirementsandunderstood.Italsodependsontheusersneedtoaddrequirementsorchangepreviouslystatedrequirements.Afterestablishinganoverallarchitectureandframework,thesystemisdevelopedanddeliveredinincrements.Usersmayexperimentwithandusedeliveredincrementswhileothersarebeingdeveloped.Forinstance,thefirstprototypemaybedeliveredthatimplementsacertainscreenwithonlysomeactivemenuitems.Whileusersareexperimentingwiththisscreenandmenuitems,otherscreensandmenuitemsareconcurrentlybeingdevelopedwhichlaterwillbecombinedwiththeexistingprototypeasitevolves.

Oncetheuserissatisfiedthattheprototypemeetsrequirements,theprototypeistransformedintothe"system".This

effortdependsonseveralfactors.Itmayincludeadding

functionalitythatwasn'tinitiallyreco

gnizedasrequired,replacinginefficientpartsoft

heprototypetomeetperformancecr

iteria,oradaptingtheprototypetofittheuser'shardware

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environment.

Prototypingcanbeginveryearly,aftersomepreliminaryrequirementsanalysishasdeterminedthebasicfunctionality,scope,andenvironmentoftheproposedsoftware.Contrarytothetraditionalwaterfallmethod,intheprototyping,functionalspecificationsarenotfixed.Rather,usersareencouragedtomodifytheirrequirementsastheythemselvesbegintounderstandthembetter.Thisisbecauseusersoftendon'treallyknowwhattheywantuntiltheyseeitonthescreen.Theprototypingprocessofdemonstration,review,andrefinementgetstheusermoreinvolvedinthedevelopmentprocess,givingthemasenseofownershipduringtheprocessandatfinalsystemdelivery.However,duetothemindsetof"prototype",usersoftenfinditdifficulttoverifythattheprototypesatisfiestheirrequirements.Therefore,guidelinesmustbeestablishedtodeterminewhentostopiteratingandtheprototypetofinalproduct.

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外文資料譯文

軟件開發(fā)概念和設(shè)計方法

在20世紀60年代，大型機和高級程序語言被用來解決包括人力資源系統(tǒng)、專有系統(tǒng)和制造系統(tǒng)等許多問題。計算機和軟件被視為解決所有商業(yè)問題的萬能藥，有時候甚至被盲目的應(yīng)用。因為很多設(shè)計上的原因，這些系統(tǒng)并不是萬能的。主要因素如下：

1．不能完全理解復(fù)雜的問題

2．沒有充分滿足終端用戶的需求，組織環(huán)境和性能折中

3．沒有準確估計開發(fā)時間和運行成本

4．缺乏一致，規(guī)范的客戶通訊框架

這個時候，結(jié)構(gòu)化的編程，自上而下設(shè)計的概念出現(xiàn)了。對軟件工程來說，結(jié)構(gòu)化編程至今仍是最重要的方法且不斷發(fā)展?！败浖こ獭备拍畹某霈F(xiàn)則是基于這樣的構(gòu)想：一個類似工程學(xué)的學(xué)科可以應(yīng)用于軟件的設(shè)計和開發(fā)。

軟件設(shè)計是一種方法，軟件設(shè)計人員可以籍此應(yīng)用技術(shù)和規(guī)則生成一種描述并定義問題解決方法的模型。最初，設(shè)計方法一直未能構(gòu)建好，而且模型也不能準確地描述軟件開發(fā)的問題。然而，隨著我們對開發(fā)過程的深入理解，設(shè)計方法已經(jīng)不斷適應(yīng)技術(shù)的變化了。

生命周期過程的模型下開發(fā)的，但人們開始嘗試尋找這種模型的替代品。

一、軟件設(shè)計基礎(chǔ)

軟件設(shè)計方法最終的目標就是向軟件設(shè)計者提供一張系統(tǒng)藍圖。它通常有三個方面：數(shù)據(jù)，構(gòu)架和過程。

．數(shù)據(jù)設(shè)計指的是數(shù)據(jù)的組織、關(guān)系、訪問和處理方法。

．構(gòu)架設(shè)計定義系統(tǒng)組件和它們之間的關(guān)系。

．過程設(shè)計建立在數(shù)據(jù)和構(gòu)架設(shè)計階段之上描述系統(tǒng)的處理細節(jié)。

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盡管設(shè)計方法眾多，但它們的基本概念非常相似。為了減少復(fù)雜度，幾乎所有軟件設(shè)計方法都把問題和軟件分割成較小的部分用于標識數(shù)據(jù)結(jié)構(gòu)、功能以及度量軟件品質(zhì)。軟件設(shè)計包括以下這些普遍原則：逐步求精、軟件構(gòu)架、程序結(jié)構(gòu)、數(shù)據(jù)結(jié)構(gòu)、軟件過程、模塊化、抽象和信息隱藏。

二、現(xiàn)代設(shè)計方法

常規(guī)的軟件開發(fā)實踐通常能被映射到傳統(tǒng)的生命階段上，包括分析、功能說明、設(shè)計、實現(xiàn)、測試和維護。然而對軟件需求的增長比軟件開發(fā)者數(shù)量增長要快，遵守常規(guī)的技術(shù)你瀑布模型）耗時太長，過多人員的參與也帶來了管理上的困難，顯然常規(guī)的思考過程對于今天的復(fù)雜信息系統(tǒng)是不夠的。因此，產(chǎn)生了許多新的軟件開發(fā)技術(shù)。最新發(fā)展出的實踐和模型井不試圖把軟件開發(fā)分割成多個階段（如說明和實現(xiàn)），而是注重于通過逐步求精和迭代把概念轉(zhuǎn)換成程序。

1、面向?qū)ο蟮募夹g(shù)

面向?qū)ο蟮能浖O(shè)計技術(shù)從根本上有別于傳統(tǒng)的設(shè)計方法。傳統(tǒng)方法中，每個模塊被當作全局過程的一個主要步驟，一步一步地往下走；而面向?qū)ο蟮脑O(shè)計圍繞著對象模型和對象所執(zhí)行的功能進行結(jié)構(gòu)化。

面向?qū)ο蟮木幊炭梢宰匪莸椒抡嬲Z言SIMULA。SIMULA是一種20世紀60年代后期的高級語言，引入了“對象類”作為封裝數(shù)據(jù)的方法。到了20世紀70年代，Smalltalk被作為一種完全的圖形用戶界面（GUI）面向?qū)ο蟮木幊汰h(huán)境被引入。甚至在30年以后，Smalltalk仍然是度量其他所有面向?qū)ο笳Z言的標準。由于面向?qū)ο蟮母拍钊遮叧墒欤罱赀@種軟件開發(fā)方法已經(jīng)流行起來。同時，軟件業(yè)注意的焦點己經(jīng)從編碼和結(jié)構(gòu)化過程轉(zhuǎn)移到通過設(shè)計和柔韌性來節(jié)省勞動力成本和時間。柔韌性變得十分關(guān)鍵，因為系統(tǒng)隨著需求的變化而快速改變：變得更大，更復(fù)雜和更不穩(wěn)定。

在面向?qū)ο笾校治龊驮O(shè)計沒有真正分開。在分析期間，系統(tǒng)對象及其特性和關(guān)系一起被確定。這些對象可以護，這樣就給整個開發(fā)過程中的所有階段提供了一種公用的語言。采用面向?qū)ο蠓椒ㄗ詈檬鞘褂脤ｉT設(shè)計的面向?qū)ο蟮拈_發(fā)工具，但是請一定記住它是一種方法而不是特指任何編程語言。許多不同的編程語言都可以用來實現(xiàn)面向?qū)ο蠹夹g(shù)和設(shè)計方法。

和過程、功能往返傳遞數(shù)據(jù)的方式不同，在面向?qū)ο蟮脑O(shè)計中，系統(tǒng)被

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看成一個由很多互相傳遞消息的對象組成的集合，每個對象都有它自己關(guān)聯(lián)操作的集合。面向?qū)ο蟮脑O(shè)計基本構(gòu)想