软件工程实践者的研究方法答案.docx

软件工程实践者的研究方法答案.docx

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软件工程实践者的研究方法答案

软件工程实践者的研究方法答案

【篇一：

外文翻译--《软件工程-实践者的研究方法》】

areengineering-apractitioner’sapproachwrittenbyrogers.pressman,ph.d.（p.340-p.343）

13.3designprinciples

softwaredesignisbothaprocessandamodel.thedesignprocessisasequenceofstepsthatenablethedesignertodescribeallaspectsofthesoftwaretobebuilt.itisimportanttonote,however,thatthedesignprocessisnotsimplyacookbook.creativeskill,pastexperience,asenseofwhatmakes“good”software,andanoverallcommitmenttoqualityarecriticalsuccessfactorsforacompetentdesign.thedesignmodelistheequivalentofanarchitect’splansforahouse.itbeginsbyrepresentingthetotalityofthethingtobebuilt（e.g.,athree-dimensionalrenderingofthehouse）andslowlyrefinesthethingtoprovideguidanceforconstructingeachdetail（e.g.,theplumbinglayout）.similarly,thedesignmodelthatiscreatedforsoftwareprovidesavarietyofdifferentviewsofthecomputersoftware.

basicdesignprinciplesenablethesoftwareengineertonavigatethedesignprocess.davissuggestsasetofprinciplesforsoftwaredesign,whichhavebeenadaptedandextendedinthefollowinglist:

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thedesignprocessshouldnotsufferfrom“tunnelvision.”agooddesignershouldconsideralternativeapproaches,judgingeachbasedontherequirementsofthetheresourcesavailabletodothejob,andthedesignconceptspresentedinsection?

thedesignshouldbetraceabletotheanalysismodel.becauseasingleelementofthedesignmodeloftentracestomultiplerequirements,itisnecessarytohaveameansfortrackinghowrequirementshavebeensatisfiedbythedesignmodel.

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thedesignshouldnotreinventthewheel.systemsareconstructedusingasetofdesignpatterns,manyofwhichhavelikelybeenencounteredbefore.thesepatternsshouldalwaysbechosenasanalternativetoreinvention.timeisshortandresourcesarelimited!

designtimeshouldbeinvestediepresentingtrulynewideasandintegratingthosepatternsthatalreadyexist.

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thedesignshould“minimizetheintellectualdistance”

betweenthesoftwareandtheproblemasitexistsintherealworld.thatis,thestructureofthesoftwaredesignshould（wheneverpossible）mimicthestructureoftheproblemdomain.

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thedesignshouldexhibituniformityandintegration.adesignisuniformifitappearsthatonepersondevelopedtheentirething.rulesofstyleandformatshouldbedefinedforadesignteambeforedesignworkbegins.adesignisintegratedifcareistakenindefininginterfacesbetweendesigncomponents.

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thedesignshouldbestructuredtoaccommodatechange.thedesignconceptsdiscussedinthenextsectionenableadesigntoachievethisprinciple.

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thedesignshouldbestructuredtodegradegently,evenwhenaberrantdata,events,oroperatingconditionsareencountered.welldesignedsoftwareshouldnever“bomb.”itshouldbedesignedtoaccommodateunusualcircumstances,andifitmustterminateprocessing,dosoinagracefulmanner.

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designisnotcoding,codingisnotdesign.evenwhendetailedproceduraldesignsarecreatedforprogramcomponents,thelevelofabstractionofthedesignmodelishigherthansourcecode.theonlydesigndecisionsmadeatthecodingleveladdressthesmallimplementationdetailsthatenabletheproceduraldesigntobecoded.

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thedesignshouldbeassessedforqualityasitisbeingcreated,notafterthefact.

avarietyofdesignconcepts（section13.4）anddesignmeasures（chapters19and24）areavailabletoassistthedesignerinassessingquality.

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thedesignshouldbereviewedtominimizeconceptual（semantic）errors.thereissometimesatendencytofocusonminutiaewhenthedesignisreviewed,missingtheforestforthetrees.adesignteamshouldensurethatmajorconceptualelementsofthedesign（omissions,ambiguity,inconsistency）havebeenaddressedbeforeworryingaboutthesyntaxofthedesignmodel.

whenthesedesignprinciplesareproperlyapplied,thesoftwareengineercreatesadesignthatexhibitsbothexternalandinternalqualityfactors.externalqualityfactorsarethosepropertiesofthesoftwarethatcanbereadilyobservedbyusers（e.g.,speed,reliability,correctness,usability）.internalqualityfactorsareofimportancetosoftwareengineers.theyleadtoahigh-qualitydesignfromthetechnicalperspective.toachieveinternalqualityfactors,thedesignermustunderstandbasicdesignconcepts.

13.4designconcepts

asetoffundamentalsoftwaredesignconceptshasevolvedoverthepastfourdecades.althoughthedegreeofinterestineachconcepthasvariedovertheyears,eachhasstoodthetestoftime.eachprovidesthesoftwaredesignerwithafoundationfromwhichmoresophisticateddesignmethodscanbeapplied.eachhelpsthesoftwareengineertoanswerthefollowingquestions:

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whatcriteriacanbeusedtopartitionsoftwareintoindividualcomponents?

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howisfunctionordatastructuredetailseparatedfromaconceptualrepresentationofthesoftware?

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whatuniformcriteriadefinethetechnicalqualityofasoftwaredesign?

m.a.jacksononcesaid:

thebeginningofwisdomfora[softwareengineer]istorecognizethedifferencebetweengettingaprogramtowork,andgettingitright.fundamentalsoftwaredesignconceptsprovidethenecessaryframeworkforgettingitright.

13.4.1abstraction

whenweconsideramodularsolutiontoanyproblem,manylevelsofabstractioncanbeposed.atthehighestlevelofabstraction,asolutionisstatedinbroadtermsusingthelanguageoftheproblemenvironment.atlowerlevelsofabstraction,amoreproceduralorientationistaken.problem-orientedterminologyiscoupledwithimplementation-orientedterminologyinanefforttostateasolution.finally,atthelowestlevelofabstraction,thesolutionisstatedinamannerthatcanbedirectlyimplemented.wassermanprovidesausefuldefinition:

thepsychologicalnotionofabstractionpermitsonetoconcentrateonaproblematsomelevelofgeneralizationwithoutregardtoirrelevantlowleveldetails;useofabstractionalsopermitsonetoworkwithconceptsandtermsthatarefamiliarintheproblemenvironmentwithouthavingtotransformthemtoanunfamiliarstructure...

eachstepinthesoftwareprocessisarefinementinthelevelofabstractionofthesoftwaresolution.duringsystemengineering,softwareisallocatedasanelementofacomputer-basedsystem.duringsoftwarerequirementsanalysis,thesoftwaresolutionisstatedintermsthatarefamiliarintheproblemenvironment.aswemovethroughthedesignprocess,thelevelofabstractionisreduced.finally,thelowestlevelofabstractionisreachedwhensourcecodeisgenerated.

aswemovethroughdifferentlevelsofabstraction,weworktocreateproceduralanddataabstractions.aproceduralabstractionisanamedsequenceofinstructionsthathasaspecificandlimitedfunction.anexampleofaproceduralabstractionwould

bethewordopenforadoor.openimpliesalongsequenceofproceduralsteps（e.g.,walktothedoor,reachoutandgraspknob,turnknobandpulldoor,stepawayfrommovingdoor,etc.）.

adataabstractionisanamedcollectionofdatathatdescribesadataobject

chapter12）.inthecontextoftheproceduralabstractionopen,wecandefineadataabstractioncalleddoor.likeanydataobject,thedataabstractionfordoorwouldencompassasetofattributesthatdescribethedoor（e.g.,doortype,swingdirection,peningmechanism,weight,dimensions）.itfollowsthattheproceduralabstractionopenwouldmakeuseofinformationcontainedintheattributesofthedataabstractiondoor.

manymodernprogramminglanguagesprovidemechanismsforcreatingabstractdatatypes.forexample,theadapackageisaprogramminglanguagemechanismthatprovidessupportforbothdataandproceduralabstraction.theoriginalabstractdatatypeisusedasatemplateorgenericdatastructurefromwhichotherdatastructurescanbeinstantiated.

controlabstractionisthethirdformofabstractionusedinsoftwaredesign.likeproceduralanddataabstraction,controlabstractionimpliesaprogramcontrolmechanismwithoutspecifyinginternaldetails.anexampleofacontrolabstractionisthesynchronizationsemaphoreusedtocoordinateactivitiesinanoperatingsystem.theconceptofthecontrolabstractionisdiscussedbrieflyinchapter14.

13.4.2refinement

stepwiserefinementisatop-downdesignstrategyoriginallyproposedbyniklauswirth.aprogramisdevelopedbysuccessivelyrefininglevelsofproceduraldetail.ahierarchyisdevelopedbydecomposingamacroscopicstatementoffunction（aproceduralabstraction）inastepwisefashionuntilprogramminglanguagestatementsarereached.anoverviewoftheconceptisprovidedbywirth:

ineachstep（oftherefinement）,oneorseveralinstructionsofthegivenprogramaredecomposedintomoredetailedinstructions.thissuccessivedecompositionorrefinementofspecificationsterminateswhenallinstructionsareexpressedintermsofanyunderlyingcomputerorprogramminglanguage...astasksarerefined,sothedatamayhavetoberefined,decomposed,orstructured,anditisnaturaltorefinetheprogramandthedataspecificationsinparallel.

everyrefinementstepimpliessomedesigndecisions.itisimportantthat...theprogrammerbeawareoftheunderlyingcriteria（fordesigndecisions）andoftheexistenceofalternativesolutions...

refinementisactuallyaprocessofelaboration.webeginwithastatementof

function（ordescriptionofinformation）thatisdefinedatahighlevelofabstraction.thatis,thestatementdescribesfunctionorinformationconceptuallybutprovidesnoinformationabouttheinternalworkingsofthefunctionortheinternalstructureoftheinformation.refinementcausesthedesignertoelaborateon