0b304軟件需求工程-lecture

Lecture6:RequirementsYanTheSchoolofSoftwareandPeKing6-LectureLecture

IntroductiontosoftwareRequirements 14-09-GoodPracticesforRequirements 14-09-LectureLectureLectureLectureLectureLectureLecture

RequirementsElicitation RequirementsSpecificationProjectandDiscussion(1)RequirementsValidationRequirementsManagement

14-09-14-10-14-10-14-10-14-11-14-11-14-11-Lecture10:ProjectandLecture11:PracticesandLecture12:

14-11-14-12-14-12-6-BusinessRules:WhatandTheSoftwareRequirementsSpecification:ATemplateTheDataSoftwareQuality6-PlayingbytheASimpleBusinessRuleBusinessRulesandTheSoftwareRequirementsASoftwareRequirementsSpecificationTheDataSoftwareQualityAttributesImportanttoAttributesImportantto6-PlayingbytheEverybusinessorganizationoperatesaccordingtoanextensivesetofcorporatepolicies,laws,andindustrystandards.Suchcontrollingprinciplesarecollectivelyknownasbusinessrules.6-PlayingbytheRulesBusinessrulesareamajorsourceofsoftwarefunctionalrequirementsbecausetheydictatecapabilitiesthatthesystemmustpossesstoconformtotherules. edbusinessrulesknownonlytoexpertsresultinaknowledgevacuumwhenthoseexpertsretireorchangejobs.6-TheRulesoftheAccordingtotheBusinessRulesGroup"Abusinessruleisastatementthatdefinesorconstrainssomeaspectofthebusiness.Itisintendedtoassertbusinessstructureortocontrolorinfluencethebehaviorofthe6-PlayingbytheASimpleBusinessRuleBusinessRulesandTheSoftwareRequirementsASoftwareRequirementsSpecificationTheDataSoftwareQualityAttributesImportanttoAttributesImportantto6-ASimpleBusinessRule6-ASimpleBusinessRuleTaxonomyThesimpleschemeshownwithfivetypesofbusinessruleswillworkformostAsixthcategoryisterms,definedwords,phrases,andabbreviationsthatareimportanttothebusiness.Aglossaryisaconvenientplacetodefine6-Factsaresimplystatementsthataretrueaboutthebusiness.OftenfactsdescribeassociationsorrelationshipsbetweenimportantbusinessFactsarealsocalledinvariants—immutabletruthsaboutdataentitiesandtheirattributes.6-FactsExamplesoffactsEverychemicalcontainerhasauniquebarcodeEveryordermusthavea Eachlineiteminanorderrepresentsaspecificcombinationofchemical,grade,containersize,andnumberofcontainers.NonrefundableticketsincurafeewhenthechangestheSalestaxisnotcomputedon 6-Constraintsrestricttheactionsthatthesystemoritsusersmayperform.Somewordsandphrasesthatsuggestsomeoneisdescribingaconstraintbusinessrulearemust,mustnot,maynot,andonly.6-ConstraintsExamplesofconstraintsAborrowerwhoislessthan18yearsoldmusthaveaparentalegalguardianascosignerontheAlibrarypatronmayplaceupto10itemsonAusermayrequestachemicalontheLevel1hazardlistonlyifhehashadhazardous-chemicaltrainingwithinthepast12Allsoftwareapplicationsmustcomplywith regulationsforusagebyvisuallyimpaired Correspondencemaynotdisplaymorethanfourdigitsofthepolicyholder'sSocialSecuritynumber.Commercialairlineflightcrewsmustreceiveatleasteightofcontinuousrestinevery24-hour6-ConstraintsManybusinessrulesimposeconstraintsonthewaythebusinessoperates.Whenevertheseconstraintsarereflectedinthesoftwarefunctionalrequirements,indicatethepertinentruleastherationaleforeachsuchderivedrequirement./6-ActionArulethattriggerssomeactivityunderspecificconditionsisanactionenabler.Astatementintheform"If<someconditionistrueorsomeeventtakesplace>,then<somethinghappens>"isacluethatsomeoneisdescribinganaction6-ActionEnablersFollowingaresomeexamplesofaction-enablingbusinessrules:Ifthechemicalstockroomhascontainersofachemicalinstock,thenofferexistingcontainerstotheIftheexpirationdateforachemicalcontainerhasbeenthennotify whocurrentlypossessesthatOnthelastdayofacalendarquarter,generatethemandatedOSHA(OccupationalSafetyandHealthAct[Administration])andEPA(EnvironmentalProtectionAgency)reportsonchemicalhandlinganddisposalforthatquarter.Ifthecustomerorderedabookbyanauthorwhohaswrittenmultiplebooks,thenoffertheauthor'sotherbookstothecustomerbeforeacceptingtheorder./6-Sometimescalledinferredknowledge,aninferenceisarulethatestablishessomenewknowledgebasedonthetruthofcertainconditions.Aninferencecreatesanewfactfromotherfactsorfromcomputations.Inferencesareoftenwritteninthe"if/then"6-InferencesSomeexamplesofinferencesIfapaymentisnotreceivedwithin30calendardaysofthedateitisdue,thentheaccountisdelinquent.Ifthevendorcannotshipanordereditemwithinfivedaysofreceivingtheorder,thentheitemisback-AcontainerofachemicalthatcanformexplosivepositionproductsisconsideredexpiredoneyearafteritsmanufactureChemicalswithanLD50toxicitylowerthan5mg/kginmiceareconsideredhazardous./6-Oneclassofbusinessrulesdefinescomputationsthatareperformedusingspecificmathematicalformulasor6-ComputationsFollowingaresomeexamplesofcomputationalbusinessrulesintextformTheunitpriceisreducedby10%forordersof6to10units,by20%ordersof11to20units,andby35%forordersofmorethan20Thedomesticground chargeforanorderthatweighsthan2poundsis$4.75plus12centsperounceoffractionThecommissionforsecuritiestradescompletedonlineis$12pertradeof1through5000shares.Thecommissionfortradesconductedthroughanaccountofficeris$45pertradeof1through5000shares.Commissionsontradesofgreaterthan5000sharesareone-halfofthesecommissions.Thetotalpriceforanorderiscomputedasthesumofthepriceoftheitemsordered,lessanyvolumediscounts,plusstateandcountysalestaxforthelocationtowhichtheorderisbeingshipped,plustheshipcharge,plusanoptionalinsurancecharge.6-ComputationsTable9-1:UsingaTabletoRepresentComputationalBusinessNumberofUnits1through06through11throughmorethan6-ingBusinessBecausebusinessrulescaninfluencemultipleapplications,organizationsshouldmanagetheirbusinessrulesasenterprise-level—notproject-level—assets.Applystructuredtemplatesfordefiningrulesofdifferenttypes.6-PlayingbytheASimpleBusinessRuleBusinessRulesandTheSoftwareRequirementsASoftwareRequirementsSpecificationTheDataSoftwareQualityAttributesImportanttoAttributesImportantto6-BusinessRulesandDependingontheapplication,sometimesyouinventbusinessrulesasyougoalongandsometimesyoudiscoverthemduringrequirementsdiscussions.Duringuserrequirementselicitationworkshops, ystcanaskquestionstoprobearoundtherationalefortherequirementsandconstraintsthatuserspresent.Thesediscussionsfrequentlysurfacebusinessrulesastheunderlyingrationale.6-Discoveringbusinessrulesbyaskingquestionsfrom 6-BusinessRulesandRequirementsAfteridentifyingand businessrules,determinewhichonesmustbeimplementedintheSomeruleswillleadtousecasesandhencetofunctionalrequirementsthatenforcetherule.6-BusinessRulesandRequirementsConsiderthefollowingthreeRule#1(actionenabler)"Iftheexpirationdateforachemicalcontainerhasbeenreached,thennotifythewhocurrentlypossessesthatRule#2(inference)"Acontainerofachemicalthatcanformexplosive positionproductsisconsideredexpiredoneyearafteritsmanufactureRule#3(fact)"Etherscanspontaneouslyformexplosiveperoxides."6-BusinessRulesandRequirementsTheserulesserveastheoriginforausecasecalled"NotifyChemicalOwnerofUseBusinessOnefunctionalrequirementforthatUseBusiness6-BusinessRulesandRequirementsYoucandefinethelinksbetweenafunctionalrequirementanditsparentbusinessrulesinthefollowingtwoways:Usearequirementattributecalled"Origin"andindicatetherulesastheoriginofthefunctionalrequirement.Definetraceabilitylinksbetweenafunctionalrequirementandthepertinentbusinessrulesintherequirementstraceabilitymatrix.6-BusinessRulesandRequirementsDatareferentialintegrityrulesfrequentlyareimplementedintheformofdatabasetriggersorstoredprocedures.Suchrulesdescribethedataupdates,insertions,anddeletionsthatthesystemmustperformbecauseofrelationshipsbetweendataentities(vonHalle2002).Forexample,thesystemmustdeleteallundeliveredlineitemsinanorderifthecustomercancelstheorder.6-BusinessRulesandRequirements ystmustdecidewhichexistingrulespertaintohisapplication,whichonesmustbeenforcedinthesoftware,andhowtoenforcethem.6-BusinessRulesandRequirementsTopreventredundancy,don'tduplicaterulesfromyourbusinessrulescatalogintheSRS.Instead,theSRSshouldreferbacktospecificrulesasthesourceofalgorithms.6-BusinessRulesandRequirementsThisapproachprovidesseveralItobviatestheneedtochangeboththebusinessruleandthecorrespondingfunctionalrequirementsiftherulechanges.ItkeepstheSRScurrentwithrulechangesbecausetheSRSsimplyreferstothemastercopyoftherule.ItfacilitatesreusingthesameruleinseveralplacesintheSRSandacrossmultipleprojectswithoutriskinganinconsistency,becausetherulesarenotburiedin ationforanysingleapplication./6-課堂討6-WhatandThevisionandscope thebusinessrequirements,andtheuserrequirementsoftenarecapturedintheformofusecases.Theproduct'sdetailedfunctionalandnonfunctionalrequirementsresideinasoftwarerequirementsspecification(SRS).6-WhatandWhere?Wecanrepresentsoftwarerequirementsinseveralways: sthatusewell-structuredandcarefullywrittennaturallanguageGraphicalmodelsthatillustratetransformationalprocesses,systemstatesandchangesbetweenthem,datarelationships,logicflows,orobjectclassesandtheirrelationshipsFormalspecificationsthatdefinerequirementsmathematicallypreciseformallogic6-RUP 6-WhatandWhere?Eventhefinestrequirementsspecificationcanneverreplaceinter aldiscussionsthroughouttheproject.It'simpossibletodiscovereveryfragmentofinformationthatfeedsintosoftwaredevelopmentupfront.Keepthecommunicationlinesopenbetweenthedevelopmentteam,customerrepresentatives,testers,andotherstakeholderssothattheycanquicklyaddressthemyriadissuesthatwillarise.6-PlayingbytheASimpleBusinessRuleBusinessRulesandTheSoftwareRequirementsASoftwareRequirementsSpecificationTheDataSoftwareQualityAttributesImportanttoAttributesImportantto6-TheSoftwareRequirementsTheSRSpreciselystatesthefunctionsandcapabilitiesthatasoftwaresystemmustprovideandtheconstraintsthatitmustrespect.TheSRSisthebasisforallsubsequentprojectplanning,design,andcoding,aswellasthefoundationforsystemtestinganduser 6-TheSoftwareRequirementsSpecification(cont’d)SeveralaudiencesrelyontheCustomers,themarketingdepartment,andsalesstaffneedtoknowwhatproducttheycanexpecttobeProjectmanagersbasetheirestimatesofschedule,effort,andresourcesontheproductdescription.TheSRS lsthesoftwaredevelopmentteamwhattoThetestinggroupusestheSRStodeveloptestplans,testcases,andprocedures.TheSRS lsmaintenanceandsupportstaffwhateachpartoftheproductissupposedtodo.6-TheSoftwareRequirementsSpecification(cont’d)SeveralaudiencesrelyontheSRS ationwritersbaseusermanualsandhelpscreensontheSRSandtheuserinterfacedesign. nelusetheSRSandationtodevelopeducationalLegalstaffensurethattherequirementscomplyapplicablelawsandSubcontractorsbasetheirworkon,andcanbeheldto,the6-TheSoftwareRequirementsSpecification(cont’d)Astheultimaterepositoryfortheproductrequirements,theSRSmustbeYoudon'thavetowritetheSRSfortheentireproductbeforebeginningdevelopment,butyoudoneedtocapturetherequirementsforeachincrementbeforebuildingthatincrement.6-TheSoftwareRequirementsSpecification(cont’d)BaseliningistheprocessoftransitioninganSRSunderdevelopmentintoonethathasbeenreviewedandapproved.6-TheSoftwareRequirementsSpecification(cont’d)Keepthefollowingrequirementsreadabilitysuggestionsinmind:Labelsections,subsections,andindividualrequirementsconsistently.Leavetextraggedontherightmargin,ratherthanfullyjustified.Usewhitespaceliberally,Usevisualemphasis(suchasbold,underline,italics,anddifferentfonts)consistentlyandjudiciously.Createatableofcontentsandperhapsanindextohelpreadersfindtheinformationtheyneed.6-TheSoftwareRequirementsSpecification(cont’d)Keepthefollowingrequirementsreadabilitysuggestionsinmind(cont’d):Numberallfiguresandtables,givethemcaptions,andrefertothembynumber.Useyourwordprocessor'scross-referencefacilityratherthanhard-codedpageorsectionnumberstorefertootherlocationswithina UsehyperlinkstoletthereaderjumptorelatedsectionsintheSRSorinother Useanappropriatetemplatetoorganizeallthenecessaryinformation./6-LabelingTosatisfythequalitycriteriaoftraceabilityandmodifiability,everyfunctionalrequirementmustbeuniquelyandpersistentlyidentified.SequenceHierarchicalTextual6-Dealing Sometimesyouknowthatyoulackapieceofinformationaboutaspecificrequirement.Youmightneedtoconsultwithacustomer,checkanexternalinterfacedescription,orbuildaprototypebeforeyoucanresolvethisUsethenotationTBD(tobedetermined)toflagtheseknowledgegaps.ResolveallTBDsbeforeimplementingasetofrequirements.6-UserInterfacesandtheIncorporatinguserinterfacedesignsintheSRShasbothdrawbacksandbenefits.6-UserInterfacesandtheSRSOntheminusscreenimagesanduserinterfacearchitecturesdescribesolutions(designs),notrequirements.

Ontheplusexploringpossibleuserinterfaces(suchaswithaworkingprototype)makestherequirementstangibletobothusersand6-UserInterfacesandtheSRSAsensiblebalanceistoincludeconceptualimages—sketches—ofselecteddisplaysintheSRSwithoutdemandingthattheimplementationpreciselyfollowthosemodels./6-PlayingbytheASimpleBusinessRuleBusinessRulesandTheSoftwareRequirementsASoftwareRequirementsSpecificationTheDataSoftwareQualityAttributesImportanttoAttributesImportantto6-6-RUP版需求規(guī)文檔概目背定義、首字母縮寫詞和縮略參考資概整體說用例模假設(shè)與依賴關(guān)具體需用例描補(bǔ)充需求[易用性、可靠性、性支持信Volere版需求規(guī)PartI：項(xiàng)目驅(qū)、項(xiàng)目的目、客戶、顧客和其他風(fēng)險(xiǎn)其他風(fēng)險(xiǎn)承擔(dān)、產(chǎn)品的用用戶和服務(wù)技術(shù)人PartII：產(chǎn)品限制條、強(qiáng)制的限制條、命名慣例和定假

PartIII：功能性需、工作的范當(dāng)前的狀工作的上下文范工作切、產(chǎn)品的范產(chǎn)品邊產(chǎn)品用單個(gè)產(chǎn)品用、功能性需求與數(shù)據(jù)需功能性需PartIV：非功能需求10、觀感需求風(fēng)格需、易用性和人性化需易于使用的需 、執(zhí)行需速度和延遲需可靠性和 性需可伸縮性和可擴(kuò)展需需ASoftwareRequirementsSpecificationTemplateManypeopleusetemplatesderivedfromtheonedescribedinIEEEStandard830-1998, mendedPracticeforSoftwareRequirementsSpecifications"(IEEE1998b).Ifyourorganizationtacklesvariouskindsorsizesofprojects,suchasnew,largesystemdevelopmentaswellasminorenhancementstolegacysystems,adoptanSRStemplateforeachmajorprojectclass.6-anSRStemplatethatwasadaptedfromtheIEEE830standardIfasectionofyourtemplatedoesn'tapplytoaparticularproject,leavethesectionheadinginplacebutindicatethatitisn'tapplicable.Thiswillkeepthereaderfromwonderingwhethersomethingimportantwasomittedinadvertently.Ifyourprojectsconsistentlyomitthesamesections,it'stimetotuneupthetemplate.6-1.TheintroductionpresentsanoverviewtohelpthereaderunderstandhowtheSRSisorganizedandhowtouseit.6-1.Introduction1.1Identifytheproductorapplicationwhoserequirementsarespecifiedinthis includingtherevisionorreleasenumber.IfthisSRSpertainstoonlypartofanentiresystem,identifythatportionorsubsystem.6-1.Introduction Describeanystandardsortypographicalconventions,includingtextstyles,highlighting,orsignificantnotations.6-1.Introduction1.3IntendedAudienceandReadingListthedifferentreaderstowhomtheSRSisDescribewhattherestoftheSRScontainsandhowitisorganized.Suggestasequenceforreadingthatismostappropriateforeachtypeofreader.6-Introduction1.4ProjectProvideashortdescriptionofthesoftwarebeingspecifiedanditspurpose.Relatethesoftwaretouserorcorporategoalsandtobusinessobjectivesandstrategies.6-Introduction1.5Listany sorotherresourcestowhichthisSRSrefers,includinghyperlinkstothemifpossible./6-OverallThissectionpresentsahigh-leveloverviewoftheproductandtheenvironmentinwhichitwillbeused,theanticipatedproductusers,andknownconstraints,assumptions,and6-OverallDescription2.1Describetheproduct'scontextand2.2ProductListthemajorfeaturestheproductcontainsorthesignificantfunctionsthatitperforms.2.3UserClassesandIdentifythevarioususerclassesthatyouanticipatewillusethisproductanddescribetheirpertinentcharacteristics.6-2.OverallDescription2.4OperatingDescribetheenvironmentinwhichthesoftwarewilloperate,includingthehardwareplatform,theoperatingsystemsandversions,andthegeographicallocationsofusers,servers,anddatabases.6-2.OverallDescription2.5DesignandImplementationDescribeanyfactorsthatwillrestricttheoptionsavailabletothedevelopersandtherationaleforeachconstraint.6-2.OverallDescription2.5DesignandImplementationConstraints(cont’d)ConstraintsmightincludetheSpecifictechnologies,tools,programminglanguages,anddatabasesthatmustbeusedorRestrictionsbecauseoftheproduct'soperatingenvironment,suchasthetypesandversionsofWebbrowsersthatwillbeused.6-2.OverallDescription2.5DesignandImplementationConstraints(cont’d)ConstraintsmightincludetheRequireddevelopmentconventionsorstandards.(Forinstance,ifthecustomer'sorganizationwillbemaintainingthesoftware,theorganizationmightspecifydesignnotationsandcodingstandardsthatasubcontractormustfollow.)BackwardcompatibilitywithearlierLimitationsimposedbybusinessrules(whichareedelsewhere).6-2.OverallDescription2.5DesignandImplementationConstraints(cont’d)ConstraintsmightincludetheHardwarelimitationssuchastimingrequirements,memoryorprocessorrestrictions,size,weight,materials,orcost.Existinguserinterfaceconventionstobefollowedwhenenhancinganexistingproduct.Standarddatainterchangeformatssuchas6-OverallDescription2.6 Listtheuser ationcomponentsthatwillbedeliveredalongwiththeexecutable2.7AssumptionsandAnassumptionisastatementthatisbelievedtobetrueintheabsenceofproofordefinitiveIdentifyanydependenciestheprojecthasonexternalfactorsoutsideitscontrol/6-System3.xSystemFeatureStatethenameofthefeatureinjustafew3.x.1DescriptionandProvideashortdescriptionofthefeatureandindicatewhetheritisofhigh,medium,orlow6-SystemFeatures3.x.2Stimulus/ResponseListthesequencesofinputstimuli(useractions,signalsfromexternaldevices,orothertriggers)andsystemresponsesthatdefinethebehaviorsforthisfeature.3.x.3FunctionalItemizethedetailedfunctionalrequirementsassociatedwiththisfeature./6-ExternalInterface4.1UserDescribethelogicalcharacteristicsofeachuserinterfacethatthesystemneeds.Somepossibleitemstoinclude4.2HardwareDescribethecharacteristicsofeachinterfacebetweenthesoftwareandhardwarecomponentsofthesystem.6-4.ExternalInterfaceRequirements4.3SoftwareDescribetheconnectionsbetweenthisproductandothersoftwarecomponents(identifiedbynameandversion),includingdatabases,operatingsystems,tools,libraries,andintegratedcommercial4.4CommunicationsStatetherequirementsforanycommunicationfunctionstheproductwilluse,includinge-mail,Webbrowser,networkcommunicationsprotocols,andelectronicforms./6-5.OtherNonfunctional5.1PerformanceStatespecificperformancerequirementsforvarioussystemoperations.5.2SafetySpecifythoserequirementsthatareconcernedwithpossibleloss,damage,orharmthatcouldresultfromtheuseofthe6-5.OtherNonfunctionalRequirements(cont’d)5.3SecuritySpecifyanyrequirementsregardingsecurity,integrity,orprivacyissuesthataffectaccesstotheproduct,useoftheproduct,andprotectionofdatathattheproductusesor5.4SoftwareQualityStateanyadditionalproductqualitycharacteristicsthatwillbeimportanttoeithercustomersordevelopers./6-6.OtherDefineanyotherrequirementsthatarenotcoveredelsewhereintheSRS.Examplesincludeinternationalizationrequirements(currency,dateformatting,language,internationalregulations,andculturalandpoliticalissues)andlegal6-AppendixA:Appendix ysisAppendixC:IssuesThisisadynamiclistoftheopenrequirementsissuesthatremaintobe6-GuidelinesforWritingThereisnoformulaicwaytowriteexcellentrequirements;thebestteacherisExcellentrequirements sfolloweffectivetechnical-writingstyleguidelinesandemployuserterminologyratherthancomputerjargon.KeepthesuggestionsinAmbiguousTermsto6-SRS6- 6-項(xiàng)目作基于IEEEStandard830模版，確定求規(guī)格說明的。6-PlayingbytheASimpleBusinessRuleBusinessRulesandTheSoftwareRequirementsASoftwareRequirementsSpecificationTheDataSoftwareQualityAttributesImportanttoAttributesImportantto6-TheDataAdatadictionary—asharedrepositorythatdefinesthemeaning,datatype,length,format,necessaryprecision,andallowedrangeorlistofvaluesforalldataelementsorattributesusedintheapplication.6-TheDataDictionaryTheinformationinthedatadictionarybindstogetherthevariousrequirementsComparedwithsprinklingdatadefinitionsthroughoutthefunctionalrequirements,aseparatedatadictionarymakesiteasytofindtheinformationyouneed,anditavoidsredundancyandinconsistencies.6-TheDataDictionaryTheitembeingdefinedisshownontheleftsideofanequalsign,withitsdefinitionontheright.Primitivedata6-TheDataDictionaryPrimitivedataAprimitivedataelementisoneforwhichno positionispossibleorRequestID=*a6-digitsystem-generatedsequentialinteger,beginningwith1,thatuniquelyidentifieseachrequest*6-TheDataDictionaryAdatastructureorrecordcontainsmultipledataitems.RequestedChemical=Chemical+Numberof+++Amount+6-TheDataDictionaryIfmultipleinstancesofanitemcanappearinadatastructure,enclosethatitemincurlyRequest=Request+Request+Charge+1:10{Requested6-TheDataDictionaryAdataelementthatcantakeonalimitednumberofdiscretevaluesiscalledanenumeratedprimitive.tyUnits=["grams"|"kilograms"|"milligrams"|*9-charactertextstringindicatingtheunitsassociatedwiththe tyofchemicalrequested*/6-PlayingbytheASimpleBusinessRuleBusinessRulesandTheSoftwareRequirementsASoftwareRequirementsSpecificationTheDataSoftwareQualityAttributesImportanttoAttributesImportantto6-BeyondFunctionality–SoftwareQualityAttributesUsersnaturallyfocusonspecifyingtheirfunctional,orbehavioral,requirements—thethingsthesoftwarewillletthemdo—butthere'smoretosoftwaresuccessthanjustdeliveringtherightfunctionality.Usersalsohaveexpectationsabouthowwelltheproductwillwork.6-BeyondFunctionality–SoftwareQualityAttributes(cont’d)Characteristicsthatfallintothiscategoryincludehoweasyitistouse,howquicklyitruns,howoftenitfails,andhowithandlesunexpectedconditions.Suchcharacteristics,collectivelyknownassoftwarequalityattributesorqualityfactors,arepartofthesystem'snonfunctional(alsocallednonbehavioral)6-BeyondFunctionality–SoftwareQualityAttributes(cont’d)Qualityattributesaredifficulttodefine,yetoftentheydistinguishaproductthatmerelydoeswhatit'ssupposedtofromonethatdelightsitscustomers.6-BeyondFunctionality–SoftwareQualityAttributes(cont’d)AsRobertCharette(1990)pointedout,"Inrealsystems,meetingthenonfunctionalrequirementsoftenismoreimportantthanmeetingthefunctionalrequirementsinthedeterminationofasystem'sperceivedsuccessorfailure."Excellentsoftwareproductsreflectanoptimumbalanceofcompetingquality6-BeyondFunctionality–SoftwareQualityAttributes(cont’d)Fromatechnical ,qualityattributesdrivesignificantarchitecturalanddesigndecisions,suchaspartitioningsystemfunctionsontovariouscomputerstoachieveperformanceorintegrityobjectives.It'sfarmoredifficultandcostlytorearchitectacompletedsystemtoachieveessentialqualitygoalsthantodesignforthemattheoutset.6-BeyondFunctionality–SoftwareQualityAttributes(cont’d)Customersgenerallydon'tpresenttheirqualityexpectationsexplicitly,althoughtheinformationtheyprovideduringelicitationssomecluesaboutwhattheyhaveinmind.Thetrickistopindownjustwhattheusersarethinkingwhentheysaythesoftwaremustbeuser-friendly,fast,reliable,or6-SoftwareQualityImportantPrimarilytoUsers

ImportantPrimarilytoDevelopers6-SoftwareQualityAttributesDifferentpartsoftheproductneeddifferentcombinationsofqualityattributes.Efficiencymightbecriticalforcertaincomponents,whileusabilityisparamountforDifferentiatequalitycharacteristicsthatapplytotheentireproductfromthosethatarespecifictocertaincomponents,certainuserclasses,orparticularusagesituations.6-SoftwareQualityAttributes anyglobalqualitygoalsinsection5.4oftheSRStemplate,andassociatespecificgoalswithindividualfeatures,usecases,orfunctional6-DefiningQuality ystscandevelopseveralpromptingquestionsbasedoneachattributethattheythoughtmightbe6-DefiningQualityForexample,toexploreintegritythey"Howimportantisittopreventusersfromviewingorderstheydidn'tplace?"or"Shouldeveryonebeabletosearchthestockroominventory?"Theyaskedtheuserrepresentativestorankeachattributeonascaleof1(don'tgiveitanotherthought)to5(critically6-PlayingbytheASimpleBusinessRuleBusinessRulesandTheSoftwareRequirementsASoftwareRequirementsSpecificationTheDataSoftwareQualityAttributesImportanttoAttributesImportantto6-AttributesImportantto6-Availabilityisameasureoftheplanneduptimeduringwhichthesystemisactuallyavailableforuseandfullyoperational.Moreformally,availabilityequalsthemeantimetofailure(MTTF)forthesystemdividedbythesumoftheMTTFandthemeantimetorepairthesystemafterafailureisencountered.Availability

MTTF+MTTR6-AvailabilityAV-1Thesystemshallbeatleast99.5percentavailableonweekdaysbetween6:00a.m.andmidnightlocaltime,andat99.95percentavailableonweekdaysbetween4:00p.m.and6:00p.m.localtime.6-Efficiencyisameasureofhowwellthesystemutilizesprocessorcapacity,diskspace,memory,orcommunicationbandwidth(Davis1993).Efficiencyisrelatedtoperformance,anotherclassofnonfunctionalrequirement,whichisdiscussedlater.6-EfficiencyEF-1.Atleast25percentoftheprocessorcapacityandRAMavailabletotheapplicationshallbeunusedattheplannedpeakload6- Alsoknownasextensibility,augmentability,extendability,andexpandability,flexibilitymeasureshoweasyitistoaddnewcapabilitiestothe6-FL-1.Amaintenanceprogrammerwhohasatleastsixmonthsofexperiencesupportingthisproductshallbeabletomakeanewoutputdeviceavailabletotheproduct,includingcodemodificationsandtesting,withnomorethanonehouroflabor.6- passessecurity,dealswithblockingunauthorizedaccesstosystemfunctions,preventinginformationloss,ensuringthatthesoftwareisprotectedfrom infection,andprotectingtheprivacyandsafetyofdataenteredintothesystem.6-IntegrityIN-1.OnlyuserswhohaveAuditoraccessprivilegesshallbeabletoviewcustomertransactionhistories./6-Interoperabilityindicateshoweasilythesystemcanexchangedataorserviceswithothersystems.6-InteroperabilityIO-1.TheChemicalTrackingSystemshallbeabletoimportanyvalidchemicalstructurefromtheChemiDraw(version2.3orearlier)andChem-Struct(version5orearlier)tools./6-Theprobabilityofthesoftwareexecutingwithoutfailureforaspecificperiodoftimeisknownasreliability(Musa,Iannino,andOkumoto1987).Robustnessissometimesconsideredanaspectofreliabil