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Sinceweselectedthesolu/onconceptinapriormodule,wenowmovefromthe

domainofthestakeholders,andbegindefiningofoursolu/onofinterest,

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Theobjec/vesofthismoduleareto:

Definehowthesolu/onwillmeetthestakeholderscapabili/es.Thesearethestakeholdersfunc/onalrequirements.

Definehowthesolu/onfitswithinthecontextorenterpriseenvironment,thatishowitwillfitwithintheopera/onalenvironment.

Capturetheusageofthesolu/on,itsbehaviorandopera/ons.Inthismodulewewillbefocusingonthecapabili/esfunc/onsthatthe

stakeholdersexpectandrequire(thisisascomparedtosystemcharacteris/cs

whichwillbeconsideredinthenextmodule).Addi/onally,weares/llconsidering

thesolu/onasablackbox.Wearedefiningcapabili/eswithinthesystem,butweare

notdefiningthesysteminternalmechanisms,architectureorcomponents.

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HereisouroverallSystemsEngineeringFrameworkflow.Wehavecompletedthe

generate,evaluateandselectsystemconceptsandinthismodulewearecovering

howtodefinethesystemscontextandsystem-levelusagesandusagescenarios

(Thesearethetwosec/onsthatareinyellowgreen)

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Completing a complete set of system requirements requires this two-prongedapproach.

In this module, we follow the upper prong and develop use cases and theassociated sequence diagrams and activity diagrams -- trace the transactions betweenthe system and the external actors/stakeholders with which it interacts for every

important scenario (including operational, maintenance, initialization, upgrade, etc.).These use cases are used to develop the input/output and functional requirements forthe system.

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Inthismodulewearegoingtoboundthesolu/on,thatis,fullyunderstand

wasisthescopeofthesystems,andwhatisoutsideofthesystem.Wearealsogoing

tounderstandwhatthesolu/onmustdo,thatis,itsfunc/ons.Wearegoingto

followthisoverallsetofsteps:

First,wewilldefinetheusagesofthesolu/on(whatisitthatthetheusers

ac/vestakeholdersofthesystemwanttodo?).Thiswillbethecapabili/esofthesystem.

Second,wewilldefinethesolu/onboundary(whataretheexternal

interfaces?).Bydefiningtheoutsideinsideofthesystem,wewillbedefining

thecontextwithinwhichthesystemoperates.

Thirdwewilldefinetheusagescenarios(howisthesolu/ongoingtobeused?)

Notethatthesestepsareo[enperformedconcurrently,andtheyarehighly

itera/ve.

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Step1definingtheusagesofthesystem.Rememberwearelookingatablackbox

viewofthesolu/on.Thatis,wedontcareaboutsolu/oninternalsatthispoint

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Todefinetheusagesofthesolu/on,wefirstmustconsider:whatmustthe

solu/ondo?Whatcapabilitymustitprovide?Thisisdescribedfromtheac/ve

stakeholdersperspec/veandcapturestheuseofthesolu/on,andthe(ac/ve)

stakeholderswithwhichitwillinteract.Theusagewilldescribesomebasic

func/onalityorcapabilityprovidedtoac/vestakeholder.

Ifyoursolu/ondirectlyinteractswithanindividual(user,maintainer,etc),theusagestypicallystartwithanac/onbytheindividual(asdescribedinthe3rdbullet).

But,dependingonhowyoursolu/onfitswithintheenvironment,ausagemaystart

withyoursystemrespondingtoaninputfromanothersystem(ifsomeexternal

systeminteractswiththeindividual)orevensomeinternalac/onfunc/on

performedbythesystemitself.

Remember,ac*vestakeholdersareindividuals,en**es,andother(external)

systemsthatinteractwithoursystemwhenitisopera*onal

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EachusageshouldcovertheWAVE:

W-Whatdoesitdo(nothow)

AfromtheAc'vestakeholderview

VprovidesValuetothestakeholder

EcoversanEn'rescenario.

Thesourceoftheseusagesarethestakeholderexpecta/onsrequirements(thecapabili/estheydescribed).Theymayneedtobeexpandedandthesetofall

usagesshouldmeetallthecapabili/esofallthestakeholders.

Foracomplexsystemthereareusuallyhundredsofusages.Oncedefined,theyare

usedlaterduringvalida/onandverifica/on,aswell.

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Inthismodulewearegoingtolookattwotoolstodefineusages:firstwewilllookat

UseCases.TheseUseCasesgraphicallydepicthowthestakeholderwillusethe

system.Theformalusecasemodeldescribestheroleoftheac/vestakeholderasthe

actor.Some/mesanac/vestakeholdermayhavedifferentroles.Itisimportantto

dis/nguishtherolesandthewaythatspecificroleinteractswiththesolu/on.

ForacomplexsystemthereareusuallyhundredsofUseCases.Theseareusedlaterduringvalida/onandverifica/on,aswell.

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Sowhatisthedefini/onofaUseCase?Presspauseandreadthroughthisslideon

yourown.

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ThisisanexampleofanATMUseCaseDiagram,atahighlevel.Notethatitcanshow

thesequen/alorderoftheusecases.Inthiscase,itshowsthattheLoginusecase

precedestheothersandtheLogoutUsecasesucceedstheothers.Althoughthebank

isdepictedasahuman,thisisreallytheATMsystem.

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Thestepstodefinethesolu/onsusages:

1.Definetheexternalinterfacesfortheopera/onalsystem.ThesearetheAc/veStakeholdersthemselvesortheActors(iftherearemul/pleroles

playedbyanAc/veStakeholders).BeclearaboutyourActordefini/onsso

thatyoucantracethemtotheac/vestakeholders.

2.Definetheusagesofeachoftheexternalinterfaces,star/ngwiththestakeholdercapabili/es(earlierintheprocess).Itisagoodideatoini/ally

focusontheusagesbythepeople.Externalsysteminterac/onsmaybea

resultofpeople(user)interac/ons.Oncethehumaninterfacesaredefined,

thendefinetheinterfaceswiththeexternalsystems.

3.Defineanyrela/onshipbetweentheusages:Areanyusagesdependentonotherusages?

4.DocumentthedetailedstepsoftheusagesviatheUseCaseDiagramandassociatedtext.

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NowletslookatanATMexampleoftheassociatedtextforawithdrawalusecase.

PresspauseandreadthisslidesothatyouunderstandhowtodiagramaUseCase

andtheassociatedtext.

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Inouroverallmoduleoutline,wearenowatStep2definingtheboundaryofthe

solu/on.Rememberwearelookingatablackboxviewofthesolu/on.Atthispoint,

wedontcareaboutanythinginternaltothesolu/on(e.g.,subsystems,hardware,

so[ware,etc)

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Nowwearegoingtolookatanimportantdiagramusedtodefineand

describethesolu/onboundaries:theContextDiagram.

TheContextDiagramisusedtoscopethesolu/onbydefiningALLofthe

solu/onsopera/onalinterfacesintoaSINGLEdiagram.Allofthepreviously-defined

usagesofthesolu/onaresummarizedinthissinglediagramandthecontextdiagram

providesasta$cviewofthesolu/on.Thecontextdiagramdefinestheinforma/onandcontrolflowsthatcrossthesolu/onboundary,thatis,itshowstheinforma/on

tofromthesystemfromoutsideofthesystem.

TheContextDiagramhighlightsseveralimportantaspectsofthesolu/on:

specificallyitillustrates,ononediagram,alloftheexternalinterfaces(human,

system,environment,asappropriate).Italsodocumentstheexternaleventsand

databothtoandfromtheoutsideworld(thatis,outsideofthesolu/on).Itdoesnot

explainwhatisinsidetheblackboxsolu/on.

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TheimportantpurposeoftheContextDiagramcanbesummarizedasonthisslide:

Firsttoclarifyandconfirmtheopera/onalenvironmentinwhichthesolu/onhasto

operate.Itisimportanttoensureunderstandingtheenterpriseormission.Oncethe

Contextisagreedtobyallstakeholdersitbecomesveryusefulformaintainingfocus

onthedevelopmenteffort,andcanhelppreventscopecreep.

SecondtheContextprovidesadiagramoftheopera$onalexternalinterfacedetailsatanadequatelevelofdetailtoallowanunderstandingofwhatthesolu/onmust

do.

Itcanalsoclarifyandverifythattheinforma/onflowsbetweenthesolu/onand

externalen//esagreewiththesystemusagesandotherbusinessormission

documenta/on.

Last,byexaminingtheinforma/onflows,andtheexternalinterfaces,theContext

Diagramprovidesanunderstandingofthefunc/onalityofthesolu/on.

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Thepurposeofthecontextdiagramistogetveryclearaboutwhatiswithin

thescopeofthesystem,whatisoutsideofthescope,andwhatexternalsystemsour

systeminteractswith.

Ac/vestakeholdersarealwaysshownbecausetheyinteractwiththesystemwhenit

isinuse(whenthesystemisopera/onal).

ContextDiagramsmayalsoshowpassivestakeholders,buttheytypicallyinfluencethesolu/on,notdirectlyinteractwithit(sotheywouldbediagrammedas

onlyinput)

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Herethereisadifferenttypeofexternalsystem.Some/mestheexternalinterface

totheenvironmentisimportanttotheunderstandingofthesystemcontext.For

exampleanycomplexsolu/onopera/nginSpace.Ifthatistrueforyoursystemof

interest,thenitshouldbeshowninthecontextdiagramandexternalinputsoutputs

wouldbedefined.

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1. Iden/fyallexternalen//es,usersandac/vestakeholdersthatneedtointerfacewiththeopera/onalsolu/on(includingtheenvironmentif

applicable).Alltheac/vestakeholdersmustbeincluded,aspreviously

defined.

2. Drawanobjectandlabelingitwiththenameofthesolu/ontobedeveloped.Thus,yoursolu/onistreatedasablackbox(asingleen/tywithnodetailsofwhatisinsideofthesolu/on).

3. Surroundthissolu/on-objectwithotherobjectslabeledwiththenamesoftheac/vestakeholders,externalsystemsandtheenvironment(ifapplicable).

Usingdifferentshapestodis/nguishdifferentcategoriescanbehelpfulin

understandingtheoverallsolu/onboundariesandinterfaces.

4. Addtheinputsandoutputsbetweenthesolu/onandtheac/vestakeholders.Theseinputsandoutputsshouldbebasedon(orsummarize)thesolu*on

usagespreviouslydefined,andmaybesummarizedtomakethediagram

morereadable.

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HereisanexampleofaContextDiagramforanATM.Thisisclearlyamore

complicatedandmorecompleteexampleofasystemcontextdiagram.Notethat

thereareuserscustomersincludingoneunfriendlycustomer,maintainers,admin,

andservicers,evenbankmanagement.

ThisslidealsoillustrateshowtoshowexternalsystemsintheContext

Diagram.SomeoftheATMstakeholdersareexternalsystems(e.g.BankorComputerNetwork)butallofthesestakeholdersareac/veones.

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Pleasereadthroughthesecaseexampleonyourown.Itprovidesastep-by-step

exampleforthismodulesteamassignment.

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Thesearetypicallyderivedfromthestakeholdercapabilityrequirements.

Ensureconsistencyandcompletenesswithyourac/vestakeholderlistand

stakeholderexpecta/onsrequirements,createdinanearliermodule.

Youmayneedtoiterateyourstakeholderlists,ac/vepassivedis/nc/onand

stakeholderexpecta/onsrequirementstoensureyouhaveaccuratelycapturedtheir

desiredcapabili/es(func/ons).

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Moredefini/onofoneofthesystemusagesinaUseCaseformatandincludingtext.

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Moredefini/onofoneofthesystemusagesinaUseCaseformatandincludingtext

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Haveyouincludedyourac/vestakeholdersfromtheearliermodule?Doyou

havenewinforma/onthatmighthavechangedapassivestakeholderintoan

ac/veone(orviceversa)?Haveyouincludedappropriateexternalsystems?

Besureyouareconsistentwiththestakeholderexpecta/onsrequirements.

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ContextDiagramonlyshowsopera/onalinterface(interfacestotheAc/ve

Stakeholders).ItmayormaynotshowinterfacestoPassiveStakeholders,sincethose

interfacesarenotopera/onalones.

Ifimportanttothesolu/on,thecontextdiagramwillalsoshowtheopera/onal

interfacetotheenvironment,butthatinterfaceisnotimportantinthisexample.