软件工程实践者的研究方法课件

1Chapter8DesignConceptsSoftwareEngineering:APractitioner’sApproach,7/e

byRogerS.Pressman1Chapter8DesignConceptsSoftw2DesignGoodsoftwaredesignshouldexhibit:Firmness(稳定性):Aprogramshouldnothaveanybugsthatinhibititsfunction.Commodity(适用性):Aprogramshouldbesuitableforthepurposesforwhichitwasintended.Delight(令人愉快):

Theexperienceofusingtheprogramshouldbepleasurableone.2DesignGoodsoftwaredesignsh3AnalysisModel=>DesignModel3AnalysisModel=>DesignMode43CharactersofDesignQualitythedesignmustimplementalloftheexplicit(明确的)requirementscontainedintheanalysismodel,anditmustaccommodatealloftheimplicit(隐含的)requirementsdesiredbythecustomer.thedesignmustbeareadable,understandableguideforthosewhogeneratecodeandforthosewhotestandsubsequentlysupportthesoftware.thedesignshouldprovideacompletepicture(全貌)ofthesoftware,addressingthedata,functional,andbehavioraldomainsfromanimplementationperspective.43CharactersofDesignQualit5QualityGuidelinesAdesignshouldexhibitanarchitecturethat(1)hasbeencreatedusingrecognizablearchitecturalstylesorpatterns,(2)iscomposedofcomponentsthatexhibitgooddesigncharacteristicsand(3)canbeimplementedinanevolutionaryfashionAdesignshouldbemodular;thatis,thesoftwareshouldbelogicallypartitionedintoelementsorsubsystemsAdesignshouldcontainrepresentationsofdata,architecture,interfaces,andcomponents.Adesignshouldleadtodatastructuresthatareappropriatefortheclassestobeimplemented.Adesignshouldleadtocomponentsthatexhibitindependentfunctionalcharacteristics.Adesignshouldleadtointerfacesthatreducethecomplexityofconnectionsbetweencomponentsandwiththeexternalenvironment.Adesignshouldbederivedusingarepeatablemethodthatisdrivenbyinformationobtainedduringsoftwarerequirementsanalysis.Adesignshouldberepresentedusinganotationthateffectivelycommunicatesitsmeaning.5QualityGuidelinesAdesignsh6DesignPrinciplesThedesignshouldbetraceabletotheanalysismodel.Thedesignshouldnotreinvent(彻底改造)thewheel.Thedesignshould“minimizethedistance”betweenthesoftwareandtheproblemasitexistsintherealworld.Thedesignshouldexhibituniformityandintegration.Thedesignshouldbestructuredtoaccommodatechange.Thedesignshouldbeassessedforqualityasitisbeingcreated,notafterthefact.Thedesignshouldbereviewedtominimizeconceptual(semantic)errors.Designisnotcoding,codingisnotdesign.FromDavis[DAV95]6DesignPrinciplesThedesigns7FundamentalConceptsAbstraction—data,procedureArchitecture(架构)—theoverallstructureofthesoftwarePatterns—conveys(承载)theessence(精髓)ofaprovendesignsolutionModularity—compartmentalization(划分)ofdataandfunctionInformationhiding—controlledinterfacesFunctionalindependence—single-mindedfunctionandlowcouplingAspects—amechanismforunderstandinghowglobalrequirementsaffectdesignRefactoring(重构)—areorganizationtechniquethatsimplifiesthedesignDesignClasses—providedesigndetailthatwillenableanalysisclassestobeimplemented7FundamentalConceptsAbstracti8DataAbstractiondoorimplementedasadatastructuremanufacturermodelnumbertypeswingdirectioninsertslightsweightopeningmechanism8DataAbstractiondoorimplement9ProceduralAbstractionopenimplementedwitha"knowledge"oftheobjectthatisassociatedwithenterdetailsofenteralgorithm9ProceduralAbstractionopenimp10Architecture“Theoverallstructureofthesoftwareandthewaysinwhichthatstructureprovidesconceptualintegrityforasystem.”Structuralproperties.

Thisaspectofthearchitecturaldesignrepresentationdefinesthecomponentsofasystem(e.g.,modules,objects)andthemannerinwhichthosecomponentsarepackagedandinteractwithoneanother.Forexample,objectsencapsulatebothdataandtheprocessingthatmanipulatesthedata.Extra-functionalproperties.Thearchitecturaldesigndescriptionshouldaddresshowthedesignarchitectureachievesrequirementsforperformance,capacity,reliability,security,adaptability,andothersystemcharacteristics.Families(族)ofrelatedsystems.Thearchitecturaldesignshoulddrawuponrepeatablepatternsthatarecommonlyencounteredinthedesignoffamiliesofsimilarsystems.Thedesignshouldhavetheabilitytoreusearchitecturalbuildingblocks.10Architecture“Theoverallstr11ArchitectureInthesimplestform,architectureisthestructureororganizationofprogramcomponents(modules),themannerinwhichthesecomponentsinteract,andthestructureofdatathatareusedbythecomponents.Inabroadersense,componentscanbegeneralizedtorepresentmajorsystemelementsandtheirinteractions.11ArchitectureInthesimplest12Modularity"modularityisthesingleattributeofsoftwarethatallowsaprogramtobeintellectuallymanageable".Monolithic(整块庞大的)software(i.e.,alargeprogramcomposedofasinglemodule)cannotbeeasilygrasped()byasoftwareengineer.Thenumberofcontrolpaths,spanofreference(引用跨度),numberofvariables,andoverallcomplexitywouldmakeunderstandingclosetoimpossible.Inalmostallinstances,youshouldbreakthedesignintomanymodules,hopingtomakeunderstandingeasierandasaconsequence,reducethecostrequiredtobuildthesoftware.12Modularity"modularityisthe13Modularity:numberofmodulesWhatisthe"right"numberofmodulesforaspecificsoftwaredesign?optimalnumberofmodulescostofsoftwarenumberofmodulesmoduleintegrationcostmoduledevelopmentcost13Modularity:numberofmodule14WhyInformationHiding?reducesthelikelihoodof“sideeffects”limitstheglobalimpactoflocaldesigndecisionsemphasizescommunicationthroughinterfacesdiscouragestheuseofglobaldataleadstoencapsulation—anattributeofhighqualitydesignresultsinhigherqualitysoftware14WhyInformationHiding?reduc15InformationHidingmoduleinterface"secret"•algorithm•datastructure•detailsofexternalinterface•resourceallocationpolicyclientsaspecificdesigndecision15InformationHidingmoduleinte16SizingModules:TwoViews16SizingModules:TwoViews17FunctionalIndependenceFunctionalindependenceisachievedbydevelopingmoduleswith"single-minded"functionandan"aversion"toexcessiveinteractionwithothermodules.Cohesion(内聚性)isanindicationoftherelativefunctionalstrengthofamodule.Acohesivemoduleperformsasingletask,requiringlittleinteractionwithothercomponentsinotherpartsofaprogram.Statedsimply,acohesivemoduleshould(ideally)dojustonething.Coupling(耦合性)isanindicationoftherelativeinterdependenceamongmodules.Couplingdependsontheinterfacecomplexitybetweenmodules,thepointatwhichentryorreferenceismadetoamodule,andwhatdatapassacrosstheinterface.17FunctionalIndependenceFunct18AspectAnaspectisarepresentationofacross-cuttingconcern.(横切关注点:利用“横切”技术，剖开封装的对象内部，将那些影响多个类的公共行为封装成一个可重用对象，称为Aspect)。ConsidertworequirementsAandB.BcrosscutsAifasoftwaredecompositionhasbeenchoseninwhichAcannotbesatisfiedwithouttakingB.AOP(AspectOrientedProgramming)是OOP的补充和完善。如：业务处理的主要流程是核心关注点，与之关系不大的部分是横切关注点,如权限认证、日志、事务处理等，可以将核心关注点和横切关注点分离开来。18AspectAnaspectisareprese19显示更新的需求：无论图元何时移动、移动到哪里，都要通知屏幕管理器（Display）其位置发生了改变。Aspect-Example19显示更新的需求：无论图元何时移动、移动到哪里，都要通知屏20采用OOP，典型做法是在每个移动图元的操作代码中，插入一段通知Display其位置发生改变的代码，即：调用Display.update()。ClassLine{privatePoint_p1,_p2;PointgetP1(){return_p1;}PointgetP2(){return_p2;}voidsetP1(Pointp1){ this._p1=p1;

Display.update();}voidsetP2(Pointp2){ this._p2=p2;

Display.update();}}ClassPoint{privateint_x1,_x2;intgetX(){return_x1;}intgetY(){return_x2;}voidsetX(intx1){ this._x1=x1;

Display.update();}voidsetY(intx2){ this._x2=x2;

Display.update();}}Aspect-Example20采用OOP，典型做法是在每个移动图元的操作代码中，21AspectDisplayUpdating{Pointcutmove():call(voidLine.setP1(Point))||call(voidLine.setP2(Point))||call(voidPoint.setX(int))||call(voidPoint.setY(int));after()returning:move(){

Display.update();}}ClassLine{

privatePoint_p1,_p2;

PointgetP1(){return_p1;}

PointgetP2(){return_p2;}

voidsetP1(Pointp1){

this._p1=p1;

}

voidsetP2(Pointp2){

this._p2=p2;

}

}

ClassPoint{

privateint_x1,_x2;

intgetX(){return_x1;}

intgetY(){return_x2;}

voidsetX(intx1){

this._x1=x1;

}

voidsetY(intx2){

this._x2=x2;

}

}

采用AOP，典型做法是在将所有移动图元的代码封装成一个Aspect:DisplayUpdating{}。Aspect-Example21AspectDisplayUpdating{Class22Aspect—AnExampleConsidertworequirementsfortheSafeHomeAWebApp.RequirementAisdescribedviatheuse-caseAccesscamerasurveillanceviatheInternet.

Adesignrefinementwouldfocusonthosemodulesthatwouldenablearegisteredusertoaccessvideofromcamerasplacedthroughoutaspace.RequirementBisagenericsecurityrequirementthatstatesthataregisteredusermustbevalidatedpriortousing

SafeHomeA.ThisrequirementisapplicableforallfunctionsthatareavailabletoregisteredSafeHomeusers.Asdesignrefinementoccurs,A*isadesignrepresentationforrequirementAandB*isadesignrepresentationforrequirementB.Therefore,A*andB*arerepresentationsofconcerns,andB*cross-cutsA*.Anaspectisarepresentationofacross-cuttingconcern.Therefore,thedesignrepresentation,B*,oftherequirement,aregisteredusermustbevalidatedpriortousing

SafeHomeA,isanaspectoftheSafeHomeWebApp.22Aspect—AnExampleConsidertw23RefactoringRefactoringistheprocessofchangingasoftwaresysteminsuchawaythatitdoesnotaltertheexternalbehaviorofthecode[design]yetimprovesitsinternalstructure.Whensoftwareisrefactored,theexistingdesignisexaminedforredundancyunuseddesignelementsinefficientorunnecessaryalgorithmspoorlyconstructedorinappropriatedatastructuresanyotherdesignfailurethatcanbecorrectedtoyieldabetterdesign.23RefactoringRefactoringisth24TheDesignModel24TheDesignModel25DesignModelElementsDataelementsDatamodel-->datastructuresDatamodel-->databasearchitectureArchitecturalelementsApplicationdomainAnalysisclasses,theirrelationships,collaborationsandbehaviorsaretransformedintodesignrealizationsInterfaceelementsComponentelementsDeploymentelements25DesignModelElementsDatael26ArchitecturalElementsThearchitecturalmodelisderivedfromthreesources:informationabouttheapplicationdomainforthesoftwaretobebuilt;specificrequirementsmodelelementssuchasdataflowdiagramsoranalysisclasses,theirrelationshipsandcollaborations.theavailabilityofarchitecturalpatterns.26ArchitecturalElementsThear27InterfaceElementsuserinterfaceexternalinterfacestoothersystems,devices.-includecheckinganddefinitiveinformationabouttheinformationissentorreceived(3)internalinterfacesbetweenvariousdesigncomponents.

-aninterfaceisasetofoperationsthatdescribessomepartofthebehaviorofaclassandprovidesaccesstotheseoperations.

27InterfaceElementsuserinter28InterfaceElements28InterfaceElements29ComponentElementscomponent-leveldesigndefinesdatastructuresforalllocaldataobjectsandalgorithmicdetailforallprocessingthatoccurswithinacomponentandaninterfacethatallowsaccesstoallcomponentoperations.29ComponentElementscomponent-30DeploymentElementsIndicatehowsoftwarefunctionalityandsubsystemswillbeallocatedwithinthephysicalcomputingenvironment30DeploymentElementsIndicate31Chapter8DesignConceptsSoftwareEngineering:APractitioner’sApproach,7/e

byRogerS.Pressman1Chapter8DesignConceptsSoftw32DesignGoodsoftwaredesignshouldexhibit:Firmness(稳定性):Aprogramshouldnothaveanybugsthatinhibititsfunction.Commodity(适用性):Aprogramshouldbesuitableforthepurposesforwhichitwasintended.Delight(令人愉快):

Theexperienceofusingtheprogramshouldbepleasurableone.2DesignGoodsoftwaredesignsh33AnalysisModel=>DesignModel3AnalysisModel=>DesignMode343CharactersofDesignQualitythedesignmustimplementalloftheexplicit(明确的)requirementscontainedintheanalysismodel,anditmustaccommodatealloftheimplicit(隐含的)requirementsdesiredbythecustomer.thedesignmustbeareadable,understandableguideforthosewhogeneratecodeandforthosewhotestandsubsequentlysupportthesoftware.thedesignshouldprovideacompletepicture(全貌)ofthesoftware,addressingthedata,functional,andbehavioraldomainsfromanimplementationperspective.43CharactersofDesignQualit35QualityGuidelinesAdesignshouldexhibitanarchitecturethat(1)hasbeencreatedusingrecognizablearchitecturalstylesorpatterns,(2)iscomposedofcomponentsthatexhibitgooddesigncharacteristicsand(3)canbeimplementedinanevolutionaryfashionAdesignshouldbemodular;thatis,thesoftwareshouldbelogicallypartitionedintoelementsorsubsystemsAdesignshouldcontainrepresentationsofdata,architecture,interfaces,andcomponents.Adesignshouldleadtodatastructuresthatareappropriatefortheclassestobeimplemented.Adesignshouldleadtocomponentsthatexhibitindependentfunctionalcharacteristics.Adesignshouldleadtointerfacesthatreducethecomplexityofconnectionsbetweencomponentsandwiththeexternalenvironment.Adesignshouldbederivedusingarepeatablemethodthatisdrivenbyinformationobtainedduringsoftwarerequirementsanalysis.Adesignshouldberepresentedusinganotationthateffectivelycommunicatesitsmeaning.5QualityGuidelinesAdesignsh36DesignPrinciplesThedesignshouldbetraceabletotheanalysismodel.Thedesignshouldnotreinvent(彻底改造)thewheel.Thedesignshould“minimizethedistance”betweenthesoftwareandtheproblemasitexistsintherealworld.Thedesignshouldexhibituniformityandintegration.Thedesignshouldbestructuredtoaccommodatechange.Thedesignshouldbeassessedforqualityasitisbeingcreated,notafterthefact.Thedesignshouldbereviewedtominimizeconceptual(semantic)errors.Designisnotcoding,codingisnotdesign.FromDavis[DAV95]6DesignPrinciplesThedesigns37FundamentalConceptsAbstraction—data,procedureArchitecture(架构)—theoverallstructureofthesoftwarePatterns—conveys(承载)theessence(精髓)ofaprovendesignsolutionModularity—compartmentalization(划分)ofdataandfunctionInformationhiding—controlledinterfacesFunctionalindependence—single-mindedfunctionandlowcouplingAspects—amechanismforunderstandinghowglobalrequirementsaffectdesignRefactoring(重构)—areorganizationtechniquethatsimplifiesthedesignDesignClasses—providedesigndetailthatwillenableanalysisclassestobeimplemented7FundamentalConceptsAbstracti38DataAbstractiondoorimplementedasadatastructuremanufacturermodelnumbertypeswingdirectioninsertslightsweightopeningmechanism8DataAbstractiondoorimplement39ProceduralAbstractionopenimplementedwitha"knowledge"oftheobjectthatisassociatedwithenterdetailsofenteralgorithm9ProceduralAbstractionopenimp40Architecture“Theoverallstructureofthesoftwareandthewaysinwhichthatstructureprovidesconceptualintegrityforasystem.”Structuralproperties.

Thisaspectofthearchitecturaldesignrepresentationdefinesthecomponentsofasystem(e.g.,modules,objects)andthemannerinwhichthosecomponentsarepackagedandinteractwithoneanother.Forexample,objectsencapsulatebothdataandtheprocessingthatmanipulatesthedata.Extra-functionalproperties.Thearchitecturaldesigndescriptionshouldaddresshowthedesignarchitectureachievesrequirementsforperformance,capacity,reliability,security,adaptability,andothersystemcharacteristics.Families(族)ofrelatedsystems.Thearchitecturaldesignshoulddrawuponrepeatablepatternsthatarecommonlyencounteredinthedesignoffamiliesofsimilarsystems.Thedesignshouldhavetheabilitytoreusearchitecturalbuildingblocks.10Architecture“Theoverallstr41ArchitectureInthesimplestform,architectureisthestructureororganizationofprogramcomponents(modules),themannerinwhichthesecomponentsinteract,andthestructureofdatathatareusedbythecomponents.Inabroadersense,componentscanbegeneralizedtorepresentmajorsystemelementsandtheirinteractions.11ArchitectureInthesimplest42Modularity"modularityisthesingleattributeofsoftwarethatallowsaprogramtobeintellectuallymanageable".Monolithic(整块庞大的)software(i.e.,alargeprogramcomposedofasinglemodule)cannotbeeasilygrasped()byasoftwareengineer.Thenumberofcontrolpaths,spanofreference(引用跨度),numberofvariables,andoverallcomplexitywouldmakeunderstandingclosetoimpossible.Inalmostallinstances,youshouldbreakthedesignintomanymodules,hopingtomakeunderstandingeasierandasaconsequence,reducethecostrequiredtobuildthesoftware.12Modularity"modularityisthe43Modularity:numberofmodulesWhatisthe"right"numberofmodulesforaspecificsoftwaredesign?optimalnumberofmodulescostofsoftwarenumberofmodulesmoduleintegrationcostmoduledevelopmentcost13Modularity:numberofmodule44WhyInformationHiding?reducesthelikelihoodof“sideeffects”limitstheglobalimpactoflocaldesigndecisionsemphasizescommunicationthroughinterfacesdiscouragestheuseofglobaldataleadstoencapsulation—anattributeofhighqualitydesignresultsinhigherqualitysoftware14WhyInformationHiding?reduc45InformationHidingmoduleinterface"secret"•algorithm•datastructure•detailsofexternalinterface•resourceallocationpolicyclientsaspecificdesigndecision15InformationHidingmoduleinte46SizingModules:TwoViews16SizingModules:TwoViews47FunctionalIndependenceFunctionalindependenceisachievedbydevelopingmoduleswith"single-minded"functionandan"aversion"toexcessiveinteractionwithothermodules.Cohesion(内聚性)isanindicationoftherelativefunctionalstrengthofamodule.Acohesivemoduleperformsasingletask,requiringlittleinteractionwithothercomponentsinotherpartsofaprogram.Statedsimply,acohesivemoduleshould(ideally)dojustonething.Coupling(耦合性)isanindicationoftherelativeinterdependenceamongmodules.Couplingdependsontheinterfacecomplexitybetweenmodules,thepointatwhichentryorreferenceismadetoamodule,andwhatdatapassacrosstheinterface.17FunctionalIndependenceFunct48AspectAnaspectisarepresentationofacross-cuttingconcern.(横切关注点:利用“横切”技术，剖开封装的对象内部，将那些影响多个类的公共行为封装成一个可重用对象，称为Aspect)。ConsidertworequirementsAandB.BcrosscutsAifasoftwaredecompositionhasbeenchoseninwhichAcannotbesatisfiedwithouttakingB.AOP(AspectOrientedProgramming)是OOP的补充和完善。如：业务处理的主要流程是核心关注点，与之关系不大的部分是横切关注点,如权限认证、日志、事务处理等，可以将核心关注点和横切关注点分离开来。18AspectAnaspectisareprese49显示更新的需求：无论图元何时移动、移动到哪里，都要通知屏幕管理器（Display）其位置发生了改变。Aspect-Example19显示更新的需求：无论图元何时移动、移动到哪里，都要通知屏50采用OOP，典型做法是在每个移动图元的操作代码中，插入一段通知Display其位置发生改变的代码，即：调用Display.update()。ClassLine{privatePoint_p1,_p2;PointgetP1(){return_p1;}PointgetP2(){return_p2;}voidsetP1(Pointp1){ this._p1=p1;

Display.update();}voidsetP2(Pointp2){ this._p2=p2;

Display.update();}}ClassPoint{privateint_x1,_x2;intgetX(){return_x1;}intgetY(){return_x2;}voidsetX(intx1){ this._x1=x1;

Display.update();}voidsetY(intx2){ this._x2=x2;

Display.update();}}Aspect-Example20采用OOP，典型做法是在每个移动图元的操作代码中，51AspectDisplayUpdating{Pointcutmove():call(voidLine.setP1(Point))||call(voidLine.setP2(Point))||call(voidPoint.setX(int))||call(voidPoint.setY(int));after()returning:move(){

Display.update();}}ClassLine{

privatePoint_p1,_p2;

PointgetP1(){return_p1;}

PointgetP2(){return_p2;}

voidsetP1(Pointp1){

this._p1=p1;

}

voidsetP2(Pointp2){

this._p2=p2;

}

}

ClassPoint{

privateint_x1,_x2;

intgetX(){return_x1;}

intgetY(){return_x2;}

voidsetX(intx1){

this._x1=x1;

}

voidsetY(intx2){

this._x2=x2;

}

}

采用AOP，典型做法是在将所有移动图元的代码封装成一个Aspect:DisplayUpdating{}。Aspect-Example21AspectDisplayUpdating{Class52Aspect—AnExampleConsidertworequirementsfortheSafeHomeAWebApp.RequirementAisdescribedviatheuse-caseAccesscamerasurveillanceviatheInternet.

Adesignrefinementwouldfocusonthosemodulesthatwouldenablearegisteredusertoaccessvideofromcamerasplacedthroughoutaspace.RequirementBisagenericsecurityrequirementthatstatesthataregisteredusermustbevalidatedpriortousing

SafeHomeA.ThisrequirementisapplicableforallfunctionsthatareavailabletoregisteredSafeHomeusers.Asdesignrefinementoccurs,A*isadesignrepresentationforrequirementAandB*isadesignrepresentationforrequirementB