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ObjectOrientedDesign(OOD):TheConcept

Objec,ves

•  Toexplainhowaso8waredesignmayberepresentedasasetofinterac;ngobjectsthatmanagetheirownstateandopera;ons

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Topicscovered

•  ObjectOrientedDevelopment(OOD)

•  Characteris,csofOOD•  BasicPrinciplesofOOD•  ObjectOrientedConcepts•  AdvantagesofOOD•  Implementa,onIssues

RECAPONSDLCPHASESVS.ARTEFACTSPRODUCED

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RecaponSDLCPhases&Artefacts

Business Domain Analysis

Requirement

Analysis

Design

Implementation

Testing & Deployment

Maintenance & Evolution

Domain Model (Class Diagram)

1) Functional & Non-Functional requirement 2) Use Case diagram

1) System Sequence Diagram 2) Activity Diagram

1) Class Diagram (refined) 2) Detail Sequence Diagram 3) State Diagram

1) Application Source Code 2) User Manual Documentation

1) Test Cases 2) Prototype

1) Change Request Form

SRS

SDD

…(zoom‐intoDesign)

• RequirementSpecifica,ons(Func,onal&Non‐Func,onal)Requirement

• RequirementModels(Use‐casesdiagram,classdiagram,ac,vitydiagram,sequencediagram)Analysis

• Architecturaldesignmodel(Packagediagram)• Detaileddesignmodels(Classdiagram(refined),sequencediagram(refined),statediagram)

Design

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ArchitecturalDesignClassifica,on

ArchitecturalDesign

SystemOrganisa.on(Style/

Pa4ern)

RepositoryModel

Client‐ServerModel

Layered(Tiers)Model

Pipe&Filter

Model‐View‐ControllerControlStyle

Model

Centralised

Call‐Return

Manager

Event‐Driven Broadcast

Interrupt‐Driven

ModularComposi.on

Object‐Oriented

Func,on‐Oriented

ArchitecturalDesignClassifica,on

ArchitecturalDesign

SystemOrganisa.on(Style/

Pa4ern)

RepositoryModel

Client‐ServerModel

Layered(Tiers)Model

Pipe&Filter

Model‐View‐ControllerControlStyle

Model

Centralised

Call‐Return

Manager

Event‐Driven Broadcast

Interrupt‐Driven

ModularComposi.on

Object‐Oriented

Func,on‐Oriented

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OBJECT‐ORIENTEDDEVELOPMENT

Object‐orientedApproach

•  Therehavebeenbasically3approachesininforma,onsystemdevelopmentarea:–  process‐oriented,–  data‐orientedand–  object‐orientedapproaches

•  Thefocusoffirsttwowaseitheronprocessordata,whiletheobject‐orientedapproachcombinesdataandprocessesintosingleen,,escalledobjects.

•  Objectsusuallycorrespondtotherealthingssuchas–  customers,suppliers,contracts,offices,vehicles

•  Thegoalofobject‐orientedapproachistomakesystemelementsmorereusable

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Object‐orienteddevelopment

•  Keyideainobjectorienteddevelopment:–  Therealworldcanbeaccuratelydescribedasa

collec,onofobjectsthatinteract.

•  Processtotransformtheanalysismodel(fromOOA)intoOODesignModel.–  FromWHAT(specifica,on)intoHOW

(implementa,on).

•  Assump,ons:–  Describinglarge,complexsystemsasinterac,ng

objectsmakethemeasiertounderstand.–  Thebehaviorsofrealworldobjectstendtobestable

over,me.–  Changestendtobelocalizedtoafewobjects.

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OOA(What?)OOD(How?)

•  SPECIFICATIONSAnalysis(OOAusingUML)

•  IMPLEMENTATIONDesign(OODusingUML)

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Characteris,csofOOD

•  OODprocessinvolvesdesigningobjectclassesandrela,onshipbetweentheseclasses.

•  Objectsareabstrac,onsofreal‐worldorsystemen,,esandmanagethemselves.

•  Objectsareindependentandencapsulatestateandrepresenta,oninforma,on.

–  Changingimplementa,on(code)ofoneobjectshouldNOTaffectothersystemobjects.

•  Systemfunc,onalityisexpressedintermsofobjectservices.

•  Shareddataareasareeliminated.•  Objectscommunicatebymessagepassing.

OOPRINCIPLES

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OODBasicPrinciples

Abstrac;on

Encapsula;on

Modularity

Polymorphism

Principle#1.Abstrac,onAbstrac,onfocusesontheessen,alcharacteris,csofsomeobject,rela,vetotheperspec,veoftheviewer.

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BasicPrinciplesofOOD:Abstrac,on

•  Abstrac,onallowsustomanagecomplexitybyconcentra,ngontheessen,alcharacteris,csthatmakesanen,tydifferentfromothers.

•  OOusesabstrac,ontodepictclassesandobjectsinasystem.

Principle#2.Encapsula,on

Encapsula,onhidesthedetailsoftheimplementa,onofanobject.

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BasicPrinciplesofOOD:Encapsula,on

•  Encapsula,onseparatestheimplementa,onofobjectsbehaviorfromitspublicinterface

•  Itiscalled“informa,onhiding”,itallowsobject’sbehaviortobeusedwithoutknowingitsimplementa,on

•  Offerstwokindsofsecurity:–  Protectsobject’sinternalstatefrombeingchangedfrom

outsideusers.–  Changescanbedonetothebehaviorimplementa,on

withoutaffec,ngotherobjects•  Ananalogy:

–  Whenyoudriveacar,youdon’thavetoknowthedetailsofhowmanycylinderstheenginehasorhowthegasolineandairaremixedandignited.

–  Insteadyouonlyhavetoknowhowtousethecontrols.

Principle#3.Modularity

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BasicPrinciplesofOOD:Modularity

•  Modularitycanbedefinedastheprocessofbreakingupofacomplexsystemintosmall,selfcontainedpiecesthatcanbemanagedeasily.

•  Packagesandsubsystemssupportthedefini,onofthemodularity.

•  Classesareindependentmodules

Principle#4.Polymorphism

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BasicPrinciplesofOOD:Polymorphism•  Polymorphism—thesamewordorphrasecanmean

differentthingsindifferentcontexts•  Analogy:inEnglish,bankcanmeansideofariveror

aplacetoputmoney(oneword,bank,butdifferentmeaningindifferentcontext)

•  InOOD,Polymorphismistheabilitytohidemanyimplementa,onsbehindthesameinterface.

•  Example:

OOCONCEPTS

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Object‐OrientedConcepts

Object Class Anribute

Opera,on Interface Package

Subsystem Rela,onships

ObjectOrientedConcepts:Object

•  Anobjectisaseparatelyiden,fiableen,tythathasasetofopera,onsandastatethatrecordstheeffectsoftheopera,ons.

•  Objectsarecharacterizedby:– state,– opera,ons,–  iden,ty.

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ObjectOrientedConcepts:Object(cont.)•  aQributes:

–  thecollec,onofinforma,onheld(i.e.,stored)bytheobject.

–  Itcanchangeover,me.–  Itchangesastheresultofanopera,onperformedontheobject.

–  Theanributeisencapsulatedwithintheobject•  opera;ons:

–  aprocedurethattakestheanributesoftheobjectandzeroormoreargumentsandchangesthestateand/orreturnsoneormorevalues.

•  iden;ty:–  awaytodis,nguishbetweentwodis,nctobjects

(eveniftheyhavethesamestateandopera,ons).

ObjectOrientedConcepts:Class

•  Aclassisatemplateforcrea,ngobjects.–  Aclassdescribesacollec,onofrelatedobjects(i.e.,instancesoftheclasses).

–  Objectsofthesameclasshavecommonopera,onsandacommonsetofpossiblestates.

–  Theconceptofclassiscloselyrelatedtotheconceptofabstractdatatypethatwediscussedpreviously.

•  Aclassisadescrip,onofasetofobjectsthatsharethesameanributes,opera,ons,rela,onships(Booch,1999).–  Anobjectisaninstanceofaclass

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ObjectOrientedConcepts:Class(cont.)

ObjectOrientedConcepts:Class(cont.)

•  InUML,aclasshas3compartments– Name

– Anributes– Opera,ons

•  Classnota,oninUML:

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ObjectOrientedConcepts:Class(Anributes)

•  Anributesisadatatypeheldbytheobjectsintheclass.

•  Onlytheobjectitselfshouldbeabletochangethevalueofitsanributes.

•  Differentobjectsofthesameclass

ObjectOrientedConcepts:Class(Opera,ons)

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ObjectOrientedConcepts:Classes&Objects

ObjectOrientedConcepts:Classes&Objects•  Aclassisanabstractdefini,onofanobject.Itdefinesthestructureandthebehaviorofeachobject.

•  Aclassistemplateforproducingobjectsofacertaintype.

•  Objectsaregroupedintoclasses

•  Anobjectisarun,meinstancesofthecorrespondingclass

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ObjectOrientedConcepts:Classes&Objects

ObjectOrientedConcepts:TerminologyRecap

•  object‐usuallyaperson,placeorthing(anoun)

•  method‐anac,onperformedbyanobject(averb)

•  class‐acategoryofsimilarobjects(suchasautomobiles)

*Classdoesnotholdanyvaluesoftheobject’sanributes

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Stereotype

•  Astereotypeisanewclassofmodelingelementthatisintroducedatmodeling,me.

•  Thestereotypeisa“tag”,orsymbol,usedtomarkthetypeofanobjectorotherconstructsothatitcanbedis,nguishedandtreateddifferentlyfromothertypesofconstructs

ObjectOrientedConcepts:Interfaces•  Aspecialclassthatcontainsacollec,onofopera,onsthatareusedtospecifyaserviceofaclass.–  Interfacesspecify,butnotimplementbehaviour.

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ObjectOrientedConcepts:Interfaces

ObjectOrientedConcepts:Interfaces(cont.)

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Abstrac,onwithInterface

ObjectOrientedConcepts:Component•  Acomponentisaphysicalandreplaceablepartofasystemthatconformstoandprovidestherealiza,onofasetofinterfaces(Booch,1999)

•  Componentmaybe:–  Sourcecodecomponent(shellscripts,datafiles,*.cpp)

–  Link,mecomponent(*.dllfiles):<<library>>–  Run,mecomponent(JavaBeans,Ac,veCcontrols,COMobjects,CORBAobjects,*.exefiles):<<applica,on>>,<<table>>

•  AcomponentenforcesEncapsula,on

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ObjectOrientedConcepts:Component(cont.)

ObjectOrientedConcepts:Packages•  Apackageisageneralpurposemechanismfor

organizingelementsintogroups(Booch,1999)•  Itisamodelelementwhichcancontainother

modelelements•  Asagroupingmechanism,doesnothaveany

seman,csdefined•  Itmaynothavearepresenta,onin

implementa,on(osenitmayrepresentadirectory)

•  Apackageownsitselements;anelementcanbelongtoonlyonepackage

•  ApackageenforcesModularity

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ObjectOrientedConcepts:Packages(cont.)

ObjectOrientedConcepts:Subsystems•  Asystemthatispartofalargersystem,and

whichhasadefiniteinterface.•  Amodelelementthathastheseman,csof

apackageandaclassthatprovidesbehavior.

•  Itimplementsoneormoreinterfaceswhichdefinethebehaviorofthesubsystem

•  AsubsystemenforcesEncapsula,on&Modularity

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ObjectOrientedConcepts:Rela,onshipbetweenClasses/Components

•  Arela,onshipisaconnec,onamongthings

•  UMLusesthesekindsofrela,onships:–  Associa,on

•  Aggrega,on•  Composi,on

–  Dependency–  Generaliza,on–  Realiza,on

ObjectOrientedConcepts:Associa,onRela,onship

•  Associa,onrepresentsageneralbinaryrela,onshipthatdescribesanac,vitybetweentwoclasses.

•  Therela,onshipallowsoneclasstocallmethodsinotherclass.

•  Whenthereisassocia,onbetweenclasses,instances/objectsoftheclasshasassocia,on.

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ObjectOrientedConcepts:Associa,onRela,onship(cont.)

Association between classes

Instance association

ObjectOrientedConcepts:Associa,onRela,onship‐Mul,plicity

•  Specifieshowmanyobjects/instancesofoneclassmayrelatetoasingleinstanceofanassociatedclass.

•  i.e.

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ObjectOrientedConcepts:Associa,onRela,onship‐Role

•  Arolenameisanamethatuniquelyiden,fiesoneendofanassocia,on.

•  Wrinennexttotheclassthatplaystherole.

•  i.e.

Student Subject take 1SCS core

ObjectOrientedConcepts:Aggrega,onRela,onship

•  Aspecialformofassocia,on.•  Representsanownershiprela,onshipsbetweentwoclasses.

•  Modelstherela,onshiplike“has‐a”,“part‐of”,“owns”.

•  Partsmaybelongtomul,plewholes.

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ObjectOrientedConcepts:Aggrega,onRela,onship(cont.)

ObjectOrientedConcepts:Composi,onRela,onship•  Modelsawhole/partrelationshipwithastrongownership;whenthewholedies,thepartdoessoaswell

•  Anobjectcanbeonlypartofonewholeobject•  Thewholepartisresponsibleforcreationanddestructionofitsparts

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ObjectOrientedConcepts:InheritanceRela,onship

•  “is‐a”or“akindof”rela,onship•  Classeswithproper,esincommoncanbegroupedsothattheircommonproper,esareonlydefinedonce.

•  Superclass:inherititsanributes&methodstothesubclass(es).

•  Subclass:inheritallitssuperclassanributes&methods+haveitsownuniqueanributes&methods.

ObjectOrientedConcepts:InheritanceRela,onship(cont.)

Sub-Class

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ObjectOrientedConcepts:InheritanceRela,onship(cont.)

•  Howdowestructuretheseclasses?

ObjectOrientedConcepts:InheritanceRela,onship(cont.)

•  Asubclassinheritsfromitssuperclass:–  attributes–  operations–  relationships.

•  Asubclassmayaddtoitsdefinition:–  Attributes–  Operations–  Relationships–  Redefineinheritedoperations

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ModelingExample

•  Modelthefollowingscenario:

– PaulaismarriedtoPaul

– Theyhavechildren

ObjectOrientedConcepts:Realiza,onRela,onship

•  Arealizationisasemanticrelationshipbetweenclassifiersinwhichoneclassifierspecifiesacontractthatanotherguarantiestocarryout.

•  Itisusedinthecontextofinterfacesandcollaborations

•  Aninterfacecanberealizedbymanyclassesorcomponents

•  Aclassmayrealizemanyinterfaces

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ObjectOrientedConcepts:DependencyRela,onship

•  Adependencyisarela,onshipthatspecifiesthatachangeinonethingmayaffectotherthingsthatuseitbutnotnecessarilytheinverse.

ObjectOrientedConcepts:DependencyRela,onship(cont.)

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AdvantagesofOOD

•  Easiermaintenance.Objectsmaybeunderstoodasstand‐aloneen,,es.

•  Objectsarepoten,allyreusablecomponents.

•  Forsomesystems,theremaybeanobviousmappingfromrealworlden,,estosystemobjects.

Implementa,onIssues

•  Reuse–  Whenyouaredevelopingsosware,youshouldmakeas

muchuseaspossibleofexis,ngcode.Soswarereuseispossibleatdifferentlevels

–  Theabstrac;onlevel:Designpanernorarchitecturalpanern

–  Theobjectlevel:directlyreuseobjectsfromlibraryratherwri,ngcodeyourself.E.g.,youneedtoprocessemailmessageinJava,youmayuseobjectsandmethodsfromJavaMaillibrary.

–  Thecomponentlevel:collec,onofobjectandobjectclasses

•  Youwritesomecode:Userinterfaceconnectedtodatabase–  Thesystemlevel: youresueen,reapplica,onsystems.

Itususallyinvolvessomeconfigura,onofthesesystems

•  Configura,onManagement:Versionmanagement,systemintegra,on(compiling),problemtracking(bugreport)

•  Host‐targetdevelopment:developmentcomputer(host),executeprogramoncomputer(target).Host&targetcomputersmaybedifferent.