Chapter_Eight.pdf system analysis and design course chapter 8

system analysis and design course chapter 8 titled determining what is build: OO Analysis

1. Chapter Eight
Determining What to Build: OO Analysis
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2. 2
SystemUseCaseModeling
SequenceDiagrams:FromUseCasestoClasses
ConceptualModeling:Classdiagrams
Activitydiagramming
UserinterfaceprototypingEvolvingyoursupplementaryspecification
ApplyingAnalysispatternsEffectively
Organizingyourmodelswithpackages
Chapter Outline
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3. Introduction
Thepurposeofanalysisistounderstandwhatwillbebuilt.
Thisissimilartorequirementsgathering.
Themaindifferenceisthat:
Thefocusofrequirementsgatheringisonunderstandingyourusersandtheirpotential
usageofthesystem,
Whereas,thefocusofanalysisshiftstounderstandingthesystemitself.
Thefollowingpicturedepictsthemainartefactsofyouranalysiseffortsandthe
relationshipsbetweenthem
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4. Overview of Analysis artifacts and their Relationships
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Thepicturehasthreeimportantimplications.
1.Analysisisaniterativeprocess.
2.Requirementsgatheringandanalysisarehighlyinterrelatedanditerative.
3.“essential”models,suchasessentialusecasemodelandessentialuserinterfaceprototype,
evolveintocorrespondinganalysisartefactsrespectively,intosystemusecasemodeland
userinterfaceprototype.
Duringanalysis,yourmaingoalistoevolveyouressentialusecasesintosystemuse
cases.
Themaindifferencebetweenanessentialusecaseandasystemusecaseis,inthe
systemusecase,youincludehigh-levelimplementationdecisions
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E.g.,asystemusecasereferstospecificuserinterfacecomponentssuchasscreens,
HTMLpages,orreports-somethingyouwouldn’tdoinanessentialusecase.
Duringanalysis,youmakedecisionsregardingwhatwillbebuiltordesign.
BecauseyourUIwillworkdifferentlydependingontheimplementationtechnology
Likewiseanessentialusecasemodel,asystemusecasemodeliscomposedofause
casediagramandtheaccompanyingdocumentationdescribingtheusecases,actors,and
associations.
Thefollowingfiguresprovidesanexampleofausecasediagram,depictsacollection
ofusecases,actors,theirassociations,asystemboundarybox(optional),andpackages
(optional).
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Therectanglearoundtheusecasesiscalledthesystemboundaryboxand,asthenamesuggests,
itdelimitsthescopeofyoursystem.
Theusecasesinsidetherectanglerepresentthefunctionalityyouintendtoimplement.
PackagesareUMLconstructsthatenableyoutoorganizemodelelements(suchasusecases)
intogroups.

8. ReuseinUseCaseModels:<<extend>>,<<include>>,andInheritance
Potentialreusecanbemodelledthroughfourgeneralizationrelationshipssupportedby
theUMLusecasemodels:
extendrelationshipsbetweenusecases,
includerelationshipsbetweenusecases,
inheritancebetweenusecases,
inheritancebetweenactors.
GoodThingstoKnowAboutUseCaseModelling
Animportantthingtounderstandaboutusecasemodelsisthattheassociations
betweenactorsandusecasesindicatetheneedforinterfaces.
Whentheactorisaperson,thentosupporttheassociation,youneedtodevelopuser
interfacecomponents,suchasscreensandreports.
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9. The Unified Modeling Language (UML)
TheUMLisagraphicallanguageforOOADthatgivesastandardwaytowritea
softwaresystem’sblueprint.
Ithelpstovisualize,specify,construct,anddocumenttheartifactsofanOOsystem.
Itisusedtodepictthestructuresandtherelationshipsinacomplexsystem.
SystemsandModelsinUML
System:Asetofelementsorganizedtoachievecertainobjectivesformasystem.
Systemsareoftendividedintosubsystemsanddescribedbyasetofmodels.
Model:Modelisasimplified,complete,andconsistentabstractionofasystem,created
forbetterunderstandingofthesystem.
View:Aviewisaprojectionofasystem’smodelfromaspecificperspective
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ConceptualModelofUML
TheConceptualModelofUMLencompassesthreemajorelements:
I.Basicbuildingblocks
II.Rules
III.Commonmechanisms
I.BasicBuildingBlocks:ThethreebuildingblocksofUMLare:
1.Things
2.Relationships
3.Diagrams
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1.Things:TherearefourkindsofthingsinUML,namely:
i.StructuralThings:ThesearethenounsoftheUMLmodelsrepresentingthestatic
elementsthatmaybeeitherphysicalorconceptual.Thestructuralthingsareclass,
object…
ii.BehavioralThings:ThesearetheverbsoftheUMLmodelsrepresentingthedynamic
behaviorovertimeandspace.
Thetwotypesofbehavioralthingsareinteractionandmachine.
iii.GroupingThings:TheycomprisetheorganizationalpartsoftheUMLmodels.Thereis
onlyonekindofgroupingthing,i.e.,package.
iv.NotationalThings:ThesearetheexplanationsintheUMLmodelsrepresentingthe
commentsappliedtodescribeelements.
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2.Relationships:Relationshipsaretheconnectionbetweenthings.
ThefourtypesofrelationshipsthatcanberepresentedinUMLare:
I.Dependency:Thisisasemanticrelationshipbetweentwothingssuchthatachangein
onethingbringsachangeintheother.
II.Association:Thisisastructuralrelationshipthatrepresentsagroupoflinkshaving
commonstructureandcommonbehavior.
III.Generalization:Thisrepresentsageneralization/specializationrelationshipinwhich
subclassesinheritstructureandbehaviorfromsuper-classes.
IV.Realization:Thisisasemanticrelationshipbetweentwoormoreclassifierssuchthat
oneclassifierlaysdownacontractthattheotherclassifiersensuretostand.
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3.Diagrams:Adiagramisagraphicalrepresentationofasystem.
Itcomprisesofagroupofelementsgenerallyintheformofagraph.
UMLincludesninediagramsinall,namely:
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1.ClassDiagram
2.ObjectDiagram
3.UseCaseDiagram
4.SequenceDiagram
6.CollaborationDiagram
6.StateChartDiagram
7.ActivityDiagram
8.ComponentDiagram
9.DeploymentDiagram

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II.Rules:UMLhasanumberofrulessothatthemodelsaresemanticallyself-consistent
andrelatedtoothermodelsinthesystemharmoniously.
UMLhassemanticrulesforthefollowing:
Names
Scope
Visibility
III.CommonMechanisms:UMLhasfourcommonmechanisms:
Specifications
Adornments
CommonDivisions
ExtensibilityMechanism
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I.Specifications:InUML,behindeachgraphicalnotation,thereisatextualstatement
denotingthesyntaxandsemantics.
II.Adornments:EachelementinUMLhasauniquegraphicalnotation.Besides,thereare
notationstorepresenttheimportantaspectsofanelementlikename,scope,visibility,etc.
III.CommonDivisions:Object-orientedsystemscanbedividedinmanyways.
Thetwocommonwaysofdivisionare:
1.Divisionofclassesandobjects:Aclassisanabstractionofagroupofsimilar
objects.Anobjectistheconcreteinstancethathasactualexistenceinthesystem.
2.DivisionofInterfaceandImplementation:Aninterfacedefinestherulesfor
interaction.
Implementationistheconcreterealizationoftherulesdefinedintheinterface.
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IV.ExtensibilityMechanisms
UMLisanopen-endedlanguage.
ItispossibletoextendthecapabilitiesofUMLinacontrolledmannertosuitthe
requirementsofasystem.
Theextensibilitymechanismsare:
Stereotypes:ItextendsthevocabularyoftheUML,throughwhichnewbuilding
blockscanbecreatedoutofexistingones.
TaggedValues:ItextendsthepropertiesofUMLbuildingblocks.
Constraints:ItextendsthesemanticsofUMLbuildingblocks.
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17. UML Basic Notations
UMLdefinesspecificnotationsforeachofthebuildingblocks.
Class:Aclassisrepresentedbyarectanglehavingthreesections:
thetopsectioncontainingthenameoftheclass
themiddlesectioncontainingclassattributes
thebottomsectionrepresentingoperationsoftheclass
Thevisibilityoftheattributesandoperationscanberepresentedinthefollowingways:
Public:Apublicmemberisvisiblefromanywhereinthesystem.Inclassdiagram,itis
prefixedbythesymbol‘+’.
Private:Aprivatememberisvisibleonlyfromwithintheclass.Itcannotbeaccessed
fromoutsidetheclass.Aprivatememberisprefixedbythesymbol‘−’.
Protected:Aprotectedmemberisvisiblefromwithintheclassandfromthesubclasses
inheritedfromthisclass,butnotfromoutside.Itisprefixedbythesymbol‘#’.
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Anabstractclasshastheclassnamewritteninitalics.
Example:LetusconsidertheCircleclassintroducedearlier.TheattributesofCircle
arex-coord,y-coord,andradius.TheoperationsarefindArea(),findCircumference(),
andscale().Letusassumethatx-coordandy-coordareprivatedatamembers,radiusis
aprotecteddatamember,andthememberfunctionsarepublic.Thefollowingfigure
givesthediagrammaticrepresentationoftheclass
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Object:Anobjectisrepresentedasarectanglewithtwosections:
Thetopsectioncontainsthenameoftheobjectwiththenameoftheclassorpackage
ofwhichitisaninstanceof.Thenametakesthefollowingforms:
object-name:class-name
object-name:class-name::package-name
class-name:incaseofanonymousobjects
Thebottomsectionrepresentsthevaluesoftheattributes.Ittakestheformattribute-
name=value.Sometimesobjectsarerepresentedusingroundedrectangles.
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Package
Apackageisanorganizedgroupofelements.
Apackagemaycontainstructuralthingslikeclasses,components,andotherpackages
init.
Notation:Graphically,apackageisrepresentedbyatabbedfolder.
Apackageisgenerallydrawnwithonlyitsname.
Howeveritmayhaveadditionaldetailsaboutthecontentsofthepackage.
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Relationship:thenotionforthedifferenttypesofrelationshipsareasfollows
Usually,elementsinarelationshipplayspecificrolesintherelationship.Arolename
signifiesthebehaviorofanelementparticipatinginacertaincontext.
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Example:Thefollowingfiguresshowexamplesofdifferentrelationshipsbetween
classes.Thefirstfigureshowsanassociationbetweentwoclasses,Departmentand
Employee,whereinadepartmentmayhaveanumberofemployeesworkinginit.
Workeristherolename.The‘1’alongsideDepartmentand‘*’alongsideEmployee
depictthatthecardinalityratioisone–to–many.Thesecondfigurerepresentsthe
aggregationrelationship,aUniversityisthe“whole–of”manyDepartments
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23. UMLstructureddiagrams
UMLstructuraldiagramsarecategorizedasfollows:classdiagram,objectdiagram,
componentdiagram,anddeploymentdiagram.
I.ClassDiagram
Aclassdiagrammodelsthestaticviewofasystem.
Itincludesoftheclasses,interfaces,andcollaborationsofasystem;andthe
relationshipsbetweenthem.
E.g.,banksystem.
Abankhasmanybranches.Ineachzone,onebranchisdesignatedasthezonalhead
officethatsupervisestheotherbranchesinthatzone.Eachbranchcanhavemultiple
accountsandloans.Anaccountmaybeeitherasavingsaccountoracurrentaccount.A
customermayopenbothasavingsaccountandacurrentaccount.Etc.
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2.ObjectDiagram:Anobjectdiagrammodelsagroupofobjectsandtheirlinksatapointoftime.
Itshowstheinstancesofthethingsinaclassdiagram.
Objectdiagramisthestaticpartofaninteractiondiagram.
Example:Thefollowingfigureshowsanobjectdiagramofaportionoftheclass
diagramoftheBankingSystem
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3.ComponentDiagram:itshowtheorganizationanddependenciesamongagroupof
components.
Componentdiagramscompriseof:
Components
Interfaces
Relationships
PackagesandSubsystems(optional)Componentdiagramsareusedfor:
Constructingsystemsthroughforwardandreverseengineering.
Modelingconfigurationmanagementofsourcecodefileswhiledevelopinga
systemusinganobject-orientedprogramminglanguage.
Representingschemasinmodelingdatabases.
Modelingbehaviorsofdynamicsystems.
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4.DeploymentDiagram:itputsemphasisontheconfigurationofruntimeprocessing
nodesandtheircomponentsthatliveonthem.
Theyarecommonlycomprisedofnodesanddependencies,orassociationsbetweenthe
nodes.
Deploymentdiagramsareusedto:
Modeldevicesinembeddedsystemsthattypicallycompriseofsoftware-intensive
collectionofhardware.
Representthetopologiesofclient/serversystems.
Modelfullydistributedsystems.
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28. UMLBehavioralDiagrams
UMLbehavioraldiagramsvisualize,specify,construct,anddocumentthedynamic
aspectsofasystem.
Thebehavioraldiagramsarecategorizedasfollows:usecasediagrams,interaction
diagrams,state–chartdiagrams,andactivitydiagrams.
UseCaseModel
UseCase:Ausecasedescribesthesequenceofactionsasystemperformsyielding
visibleresults.
Itshowstheinteractionofthingsoutsidethesystemwiththesystemitself.Usecases
maybeappliedtothewholesystemaswellasapartofthesystem.
Actor:Anactorrepresentstherolesthattheusersoftheusecasesplay.Anactormay
beaperson(e.g.student,customer),adevice(e.g.workstation),oranother.
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ThefollowingfigureshowsthenotationsofanactornamedStudentandausecase
calledGeneratePerformanceReport
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5.UseCaseDiagrams
Usecasediagramspresentanoutsideviewofthemannertheelementsinasystem
behaveandhowtheycanbeusedinthecontext.
Usecasediagramscompriseof:
Usecases
Actors
Relationshipslikedependency,generalization,andassociationUsecasediagrams
areused:
Modelthecontextofasystembyenclosingalltheactivitiesofasystemwithina
rectangleandfocusingontheactorsoutsidethesystembyinteractingwithit.
Tomodeltherequirementsofasystemfromtheoutsidepointofview
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E.g.,LetusconsideranAutomatedTradingHouseSystem.Weassumethefollowing
featuresofthesystem:
Thetradinghousehastransactionswithtwotypesofcustomers,individual
customersandcorporatecustomers.
Oncethecustomerplacesanorder,itisprocessedbythesalesdepartmentandthe
customerisgiventhebill.
Thesystemallowsthemanagertomanagecustomeraccountsandanswerany
queriespostedbythecustomer.
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InteractionDiagrams:itdepictinteractionsofobjectsandtheirrelationships.
Theyalsoincludethemessagespassedbetweenthem.Therearetwotypesofinteraction
diagrams:
SequenceDiagramsandCollaborationDiagrams
Interactiondiagramsareusedformodeling:
thecontrolflowbytimeorderingusingsequencediagrams.
thecontrolflowoforganizationusingcollaborationdiagrams.
6.SequenceDiagrams:areinteractiondiagramsthatillustratetheorderingofmessages
accordingtotime.
Notations:Thesediagramsareintheformoftwo-dimensionalcharts.Theobjectsthat
initiatetheinteractionareplacedonthex–axis.
Themessagesthattheseobjectssendandreceiveareplacedalongthey-axis,inthe
orderofincreasingtimefromtoptobottom
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E.g.,AsequencediagramfortheAutomatedTradingHouseSystemisshowninthe
followingfigure.
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7.CollaborationDiagramsareinteractiondiagramsthatillustratethestructureofthe
objectsthatsendandreceivemessages.
Notations:Inthesediagrams,theobjectsthatparticipateintheinteractionareshown
usingvertices.
Thelinksthatconnecttheobjectsareusedtosendandreceivemessages.Themessageis
shownasalabeledarrow.
Example:CollaborationdiagramfortheAutomatedTradingHouseSystemis
illustratedinthefigurebelow
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8.State–ChartDiagrams
Astate–chartdiagramshowsastatemachinethatdepictsthecontrolflowofanobject
fromonestatetoanother.
Astatemachinedepictsthesequencesofstateswhichanobjectundergoesdueto
eventsandtheirresponsestoevents.
State–ChartDiagramsincludeof:
States:SimpleorComposite
Transitionsbetweenstates
Eventscausingtransitions
Actionsduetotheevents
State-chartdiagramsareusedformodelingobjectswhicharereactiveinnature
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Example,IntheAutomatedTradingHouseSystem,letusmodelOrderasanobject
andtraceitssequence.Thefollowingfigureshowsthecorrespondingstate–chart
diagram.
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9.ActivityDiagrams:Anactivitydiagramdepictstheflowofactivitieswhichare
ongoingnon-atomicoperationsinastatemachine.
Activitiesresultinactionswhichareatomicoperations.
Activitydiagramsincludeof:
Activitystatesandactionstates
Transitions
Objects
Activitydiagramsareusedformodeling:
Workflowsasviewedbyactors,interactingwiththesystem.
detailsofoperationsorcomputationsusingflowcharts.
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Example,ThefollowingfigureshowsanactivitydiagramofaportionoftheAutomated
TradingHouseSystem.
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39. End of chapter Eight
Any Question?
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