软件工程2012SEModule2

SoftwareRequirements,Objectives,TointroducetheconceptsofuserandsystemrequirementsTodescribefunctionalandnon-functionalrequirementsToexplainhowsoftwarerequirementsmaybeorganisedinarequirementsdocument,Topicscovered,Functionalandnon-functionalrequirementsUserrequirementsSystemrequirementsInterfacespecificationThesoftwarerequirementsdocument,Typesofrequirement,UserrequirementsStatementsinnaturallanguageplusdiagramsoftheservicesthesystemprovidesanditsoperationalconstraints.Writtenforcustomers.SystemrequirementsAstructureddocumentsettingoutdetaileddescriptionsofthesystemsfunctions,servicesandoperationalconstraints.Defineswhatshouldbeimplementedsomaybepartofacontractbetweenclientandcontractor.,Functionalandnon-functionalrequirements,FunctionalrequirementsStatementsofservicesthesystemshouldprovide,howthesystemshouldreacttoparticularinputsandhowthesystemshouldbehaveinparticularsituations.Non-functionalrequirementsconstraintsontheservicesorfunctionsofferedbythesystemsuchastimingconstraints,constraintsonthedevelopmentprocess,standards,etc.DomainrequirementsRequirementsthatcomefromtheapplicationdomainofthesystemandthatreflectcharacteristicsofthatdomain.,Functionalrequirements,Describefunctionalityorsystemservices.Dependonthetypeofsoftware,expectedusersandthetypeofsystemwherethesoftwareisused.Functionaluserrequirementsmaybehigh-levelstatementsofwhatthesystemshoulddobutfunctionalsystemrequirementsshoulddescribethesystemservicesindetail.,Requirementsimprecision,Problemsarisewhenrequirementsarenotpreciselystated.Ambiguousrequirementsmaybeinterpretedindifferentwaysbydevelopersandusers.ConsiderthetermappropriateviewersUserintention-specialpurposeviewerforeachdifferentdocumenttype;Developerinterpretation-Provideatextviewerthatshowsthecontentsofthedocument.,Requirementscompletenessandconsistency,Inprinciple,requirementsshouldbebothcompleteandconsistent.CompleteTheyshouldincludedescriptionsofallfacilitiesrequired.ConsistentThereshouldbenoconflictsorcontradictionsinthedescriptionsofthesystemfacilities.Inpractice,itisimpossibletoproduceacompleteandconsistentrequirementsdocument.,Non-functionalrequirements,Thesedefinesystempropertiesandconstraintse.g.reliability,responsetimeandstoragerequirements.ConstraintsareI/Odevicecapability,systemrepresentations,etc.ProcessrequirementsmayalsobespecifiedmandatingaparticularCASEsystem,programminglanguageordevelopmentmethod.Non-functionalrequirementsmaybemorecriticalthanfunctionalrequirements.Ifthesearenotmet,thesystemisuseless.,Non-functionalclassifications,ProductrequirementsRequirementswhichspecifythatthedeliveredproductmustbehaveinaparticularwaye.g.executionspeed,reliability,etc.OrganisationalrequirementsRcessstandardsused,implementationrequirements,etc.ExternalrequirementsReroperabilityrequirements,legislativerequirements,etc.,Non-functionalrequirementtypes,Goalsandrequirements,Non-functionalrequirementsmaybeverydifficulttostatepreciselyandimpreciserequirementsmaybedifficulttoverify.GoalAgeneralintentionoftheusersuchaseaseofuse.Verifiablenon-functionalrequirementAstatementusingsomemeasurethatcanbeobjectivelytested.Goalsarehelpfultodevelopersastheyconveytheintentionsofthesystemusers.,Examples,AsystemgoalThesystemshouldbeeasytousebyexperiencedcontrollersandshouldbeorganisedinsuchawaythatusererrorsareminimised.Averifiablenon-functionalrequirementExperiencedcontrollersshallbeabletouseallthesystemfunctionsafteratotaloftwohourstraining.Afterthistraining,theaveragenumberoferrorsmadebyexperiencedusersshallnotexceedtwoperday.,Requirementsinteraction,Conflictsbetweendifferentnon-functionalrequirementsarecommonincomplexsystems.SpacecraftsystemTominimiseweight,thenumberofseparatechipsinthesystemshouldbeminimised.Tominimisepowerconsumption,lowerpowerchipsshouldbeused.However,usinglowpowerchipsmaymeanthatmorechipshavetobeused.Whichisthemostcriticalrequirement?,Userrequirements,Shoulddescribefunctionalandnon-functionalrequirementsinsuchawaythattheyareunderstandablebysystemuserswhodonthavedetailedtechnicalknowledge.Userrequirementsaredefinedusingnaturallanguage,tablesanddiagramsasthesecanbeunderstoodbyallusers.,Systemrequirements,Moredetailedspecificationsofsystemfunctions,servicesandconstraintsthanuserrequirements.Theyareintendedtobeabasisfordesigningthesystem.Theymaybeincorporatedintothesystemcontract.SystemrequirementsmaybedefinedorillustratedusingsystemmodelsdiscussedinChapter8.,Problemswithnaturallanguage,LackofclarityPrecisionisdifficultwithoutmakingthedocumentdifficulttoread.RequirementsconfusionFunctionalandnon-functionalrequirementstendtobemixed-up.RequirementsamalgamationSeveraldifferentrequirementsmaybeexpressedtogether.,Graphicalmodels,Graphicalmodelsaremostusefulwhenyouneedtoshowhowstatechangesorwhereyouneedtodescribeasequenceofactions.DifferentgraphicalmodelsareexplainedinChapter8.,EventsandUseCases,EventTableacatalogofusecaseslistedbyevent.ContainsdetailedinformationTriggerasignalthatindicatesaneventhasoccurredSourceanexternalagentthatinitiateseventandsuppliesdatafortheeventResponseanoutputproducedbythesystemDestinationanexternalagentthatreceivestheresponse,TypesofEvents,ExternalOutsidesystemInitiatedbyexternalagentoractorTemporalOccurasresultofreachingapointintimeBasedonsystemdeadlinesStateSomethinginsidesystemtriggersprocessingneed,EventTable,AUseCase/ScenarioView,UsecaseanalysisusedtoidentifyanddefineallbusinessprocessesthatsystemmustsupportUsecaseanactivityasystemcarriedout,usuallyinresponsetoauserrequestActorRoleplayedbyuserOutsideautomationboundary,UseCasewithanActor,UseCaseDiagram,UseCasesofSubsystem,Relationship,DocumentssituationinwhichoneusecaserequirestheservicesofacommonsubroutineAnotherusecaseisdevelopedforthiscommonsubroutineAcommonusecasecanbereusedbymultipleusecasesandmayormaynotbelinkeddirectlywithanactor.SituationwheretheextrausecaseprocessingisMandatory.Theusecaseisalwaysused,SubsystemwithUseCases,extend,generalization,UseCaseDescriptions,UsecasedescriptionadescriptionoftheprocessingstepsforausecaseActorapersonorthingthatusesthesystem.ActorshavecontactwiththesystemScenarioorInstanceaparticularsetofinternalstepsthatrepresentauniquepathoftheusecaseThreetypesofdescriptionsBriefdescriptionIntermediatedescriptionFullydevelopeddescription,BriefDescription,IntermediateDescription,FullyDevelopedDescription,TheDomainModelClassDiagram,UnifiedModellingLanguage(UML)diagramDomainmodelclassdiagramModelsthingsintheusersworkdomainUsedtodefinerequirementsforOO(verysimilartoentitiesinERD),UMLClassSymbol,SimpleDomainModelClassDiagram,MultiplicityofAssociations,UniversityCourseEnrolmentDomainModelClassDiagram,RefinedModelwithAssociationClassandGradeAttribute,MoreComplexClassConcepts,Generalization/specializationhierarchiesGeneralsuperclassestospecializedsubclassesInheritanceallowssubclassestosharecharacteristicsoftheirsuperclasses,AGeneralization/SpecializationClassHierarchyforMotorVehicles,Whole-PartHierarchies,Whole-parthierarchieshierarchiesthatstructureclassesbycomponentsAggregationwhole-partrelationshipsbetweenobjectanditsremovablepartsPartscanexistseparatelyLikecaranditstiresCompositionwhole-partrelationshipsbetweenobjectanditsnon-removableparts.PartscannotexistseparatelyLikeHandiscomposedoffingersandthumb,Whole-PartAggregationRelationships,ObjectDiagram,Sequencediagrams,Theseshowthesequenceofeventsthattakeplaceduringsomeuserinteractionwithasystem.Youreadthemfromtoptobottomtoseetheorderoftheactionsthattakeplace.,SequencediagramofATMwithdrawal,CashwithdrawalfromanATMValidatecard;Handlerequest;Completetransaction.,CollaborationDiagram,StateChartDiagram,Bookingfilmtickets,ActivityDiagram,Basicsymbol,transition,Branch,join,Branchandjoin,publicclassassistantpublicintid;publicintmax(intscore1,intscore2,intscore3)inttemp;temp=score1;if(score2temp)temp=score2;if(score3temp)temp=score3;returntemp;,furcation,confluence,Example-Mp3Player,UseCase,ActivityDiagram,swimlane,activitydiagram:,swimlane:,Interfacespecification,Mostsystemsmustoperatewithothersystemsandtheoperatinginterfacesmustbespecifiedaspartoftherequirements.ThreetypesofinterfacemayhavetobedefinedProceduralinterfaces;Datastructuresthatareexchanged;Datarepresentations.Formalnotationsareaneffectivetechniqueforinterfacespecification.,Therequirementsdocument,Therequirementsdocumentistheofficialstatementofwhatisrequiredofthesystemdevelopers.Shouldincludebothadefinitionofuserrequirementsandaspecificationofthesystemrequirements.ItisNOTadesigndocument.Asfaraspossible,itshouldsetofWHATthesystemshoulddoratherthanHOWitshoulddoit,IEEErequirementsstandard,Defines