SoftwareEngineering

UsmanFarooq

sf_usman@

Goal(s)ofthislecture

TounderstandrequirementsanalysisStagesinrequirementsanalysisTechniquesusedforperformingrequirementsanalysisTounderstandrequirementsnegotiationRequirementsnegotiationstages2

RequirementsAnalysisTheaimofrequirementsanalysisistodiscoverproblemswiththesystemrequirements,especiallyincompletenessandinconsistencies.Someanalysisisinter-leavedwithrequirementselicitation,asproblemsaresometimesobviousassoonasarequirementisexpressed.

RequirementsAnalysisRequirementsElicitationRequirementsAnalysisDraftStatementofRequirementsRequirementsProblemsRequirementsNegotiationRequirementsDocuments4

RequirementsAnalysisAnalystsreadtherequirements,highlightproblems,anddiscusstheminrequirementsreviewmeetingsThisisatime-consumingandexpensiveactivity5

StagesofRequirementsAnalysisNecessitycheckingConsistencyandcompletenesscheckingFeasibilitycheckingUnnecessaryrequirementsConflictingandincompleterequirementsInfeasiblerequirementsRequirementsAnalysis6

RequirementsAnalysisStagesFromthediagramshowninpreviousslide,itisclearthattherearethreestagesofrequirementsanalysisprocess:NecessitycheckingConsistencyandcompletenesscheckingFeasibilitychecking7

RequirementsAnalysisStages1)NecessityCheckingTheneedfortherequirementisanalyzed.Insomecases,requirementsmaybeproposedwhichdon’tcontributetothebusinessgoalsoftheorganizationortothespecificproblemtobeaddressedbythesystem.8

RequirementsAnalysisStages2)ConsistencyandCompletenessCheckingTherequirementsarecross-checkedforconsistencyandcompleteness.Consistencymeansthatnorequirementsshouldbecontradictory;Completenessmeansthatnoservicesorconstraintswhichareneededhavebeenmissedout.9

RequirementsAnalysisStages3)FeasibilityCheckingTherequirementsarecheckedtoensurethattheyarefeasibleinthecontextofthebudgetandscheduleavailableforthesystemdevelopment.10

RequirementsAnalysisTechniquesAnalysischecklistsAchecklistisalistofquestionswhichanalystsmayusetoassesseachrequirementInteractionmatricesInteractionmatricesareusedtodiscoverinteractionsbetweenrequirementsandtohighlightconflictsandoverlaps11

RequirementsAnalysisTechniques1)AnalysischecklistsEachrequirementmaybeassessedagainstthechecklistWhenpotentialproblemsarediscovered,theseshouldbenotedcarefullyTheycanbeimplementedasaspreadsheet,wheretherowsarelabeledwiththerequirementsidentifiersandcolumnsarethe

checklistitems12

RequirementsAnalysisTechniques1)AnalysischecklistsExamplesRequirementsambiguityIstherequirementambiguousi.e.,coulditbereadindifferentwaysbydifferentpeople?Whatarethepossibleinterpretationsoftherequirement?

RequirementsrealismIstherequirementrealisticgiventhetechnologywhichwillbeusedtoimplementthesystem?RequirementstestabilityIstherequirementtestable,thatis,isitstatedinsuchawaythattestengineerscanderiveatestwhichcanshowifthesystemmeetsthatrequirement?13

RequirementsAnalysisTechniques2)InteractionmatricesAveryimportantobjectiveofrequirementsanalysisistodiscovertheinteractionsbetweenrequirementsandtohighlightrequirementsconflictsandoverlapsArequirementsinteractionmatrixshowshowrequirementsinteractwitheachother,whichcanbeconstructedusingaspreadsheet14

RequirementsAnalysisTechniques2)Interactionmatrices(Continuous)Eachrequirementiscomparedwithotherrequirements,andthematrixisfilledasfollows:Forrequirementswhichconflict,fillina1Forrequirementswhichoverlap,fillina1000Forrequirementswhichareindependent,fillina015

RequirementsAnalysisTechniques2)Interactionmatrices(Continuous)ConsideranexampleRequirementR1R2R3R4R5R6R1001000011R2000000R3100000100001000R4001000011R5100100R610100010016

RequirementsAnalysisTechniques2)Interactionmatrices(Continuous)ConsideranexampleIntheexample,weareconsidering,wecanseethatR1overlapswithR3andconflictswithR5andR6R2isanindependentrequirementR3overlapswithR1,R4,andR617

RequirementsAnalysisTechniques2)Interactionmatrices(Continuous)TheadvantageofusingnumericvaluesforconflictsandoverlapsisthatyoucansumeachrowandcolumntofindthenumberofconflictsandthenumberofoverlapsRequirementswhichhavehighvaluesforoneorbothofthesefiguresshouldbecarefullyexaminedAlargenumberofconflictsoroverlapsmeansthatanychangestothatrequirementwillprobablyhaveamajorimpactoftherestoftherequirementsInteractionmatricesworkonlywhenthereisrelativelysmallnumberofrequirements,aseachrequirementiscomparedwitheveryotherrequirement18

RequirementsAnalysisTechniques2)Interactionmatrices(Continuous)Note:“Theseoverlapsandconflictshavetobe discussedandresolvedduringrequirements negotiation,whichwe’lldiscussnext”19

RequirementsNegotiationDisagreementsaboutrequirementsareinevitablewhenasystemhasmanystakeholders.Conflictsarenot‘failures’butreflectdifferentstakeholderneedsandprioritiesRequirementsnegotiationistheprocessofdiscussingrequirementsconflictsandreachingacompromisethatallstakeholderscanagreeto20

RequirementsNegotiationInplanningarequirementsengineeringprocess,itisimportanttoleaveenoughtimefornegotiation.Findinganacceptablecompromisecanbetime-consuming.Thefinalrequirementswillalwaysbeacompromisewhichisgovernedbytheneedsoftheorganizationingeneral,thespecificrequirementsofdifferentstakeholders,designandimplementationconstraints,andthebudgetandscheduleforthesystemdevelopment21

RequirementsNegotiationStagesRequirementsdiscussionRequirementsprioritizationRequirementsagreementRequirementsNegotiationUnnecessaryrequirementsConflictingandincompleterequirementsInfeasiblerequirements