Writing Effective Requirements Specifications Pres

WritingEffectiveRequirementsSpecificationsPresenter:WilliamM.WilsonTrack:Track4Day:WednesdayKeywords:Requirements,Documentation,SpecificationPracticesAbstractTheGoddardSpaceFlightCenter's(GSFC)SoftwareAssuranceTechnologyCenter(SATC)hasdevelopedanearlylifecycletoolforassessingrequirementsthatarespecifiedinnaturallanguage.TheAutomatedRequirementsMeasurement(ARM)toolwasusedtoanalyzemorethan50NASASystem/SoftwareRequirementsSpecification(SRS)documents.ARMreportswereusedtofocushumananalysisonspecificaspectsofthedocumentationpracticesexhibitedbythesedocuments.Severalsignificantweaknesseswereidentified.Thispaperidentifiestheunderlyingproblemsthatproducethesedeficienciesandrecommendsmethodsthatcanbeusedtopreventsuchproblems.1.IntroductionThispaperisbasedontheresultsofaSATCstudyofNASAsystem/softwarerequirementsspecification(SRS)documentswritteninnaturallanguage.InitialsectionsofthispaperdefinetheSoftwareAssuranceTechnologyCenter's(SATC)organizationalandmissioncontextanditsapproachtotheSRSstudy.Resultsofthestudy,thedocumentationdeficienciesfoundandtheircausesarediscussedinthebodyofthispaper.ThefinalsectionofthispaperpresentsrecommendeddocumentationpracticesthatwillprecludethetypesofproblemsfoundbytheSATC'sSRSstudy.Despitethesignificantadvantagesattributedtotheuseofformalspecificationlanguages,theirusehasnotbecomecommonpractice.Becausetherequirementsthattheacquirerexpectsthedevelopertocontractuallysatisfymustbeunderstoodbybothparties,specificationsaremostoftenwritteninnaturallanguage.Theuseofnaturallanguagetoprescribecomplex,dynamicsystemshasatleastthreesevereproblems:ambiguity,inaccuracyandinconsistency[11].Definingalarge,multi-dimensionalcapabilitywithinthelimitationsimposedbythetwodimensionalstructureofadocumentcanobscuretherelationshipsbetweengroupsofrequirements.Theimportanceofcorrectlydocumentingrequirementshascausedthesoftwareindustrytoproduceasignificantnumberofaids[3]tothecreationandmanagementoftherequirementsspecificationdocumentsandindividualspecificationsstatements.Veryfewoftheseaidsassistinevaluatingthequalityoftherequirementsdocumentortheindividualspecificationstatements.ThissituationmotivatedtheSATCtodevelopatooltoprovidemetricsthatNASAprojectmanagerscanusetoassessthequalityoftheirrequirementsspecificationdocumentsandtoidentifyrisksthatpoorlyspecifiedrequirementswillintroduceintotheirproject.Itmustbeemphasizedthatthetooldoesnotattempttoassessthecorrectnessoftherequirementsspecified.Itassessesthestructureoftherequirementsdocumentandindividualspecificationstatementsandthevocabularyusedtostatetherequirements.Thedevelopmentofthistoolhasleadtoanin-depthstudyofthedocumentsusedtoevolveandtestitscapabilities.ThisstudyhighlightedthemostcommondeficienciesfoundinSRSs.Thesedeficienciesweresopervasivethateffortstoidentifytheunderlyingproblemsandpotentialsolutionswereinitiated.2.BackgroundTwoofNASA'sninemajorfieldinstallationshaveprimaryresponsibilitiesforunmannedspaceexplorationmissions.GoddardSpaceFlightCenter's(GSFC)areaofresponsibilityisnear-Earthmissions,whiletheJetPropulsionLaboratory(JPL)isresponsiblefordeepspacemissions.GSFC'smissionsareimplementedbytheFlightProjectsDirectorate.TheMissionOperationsandDataSystemsDirectorate(MODSD)providesGSFCflightprojectswithinstitutionalcommunicationsanddatahandlingsupportsystems.TheOfficeofFlightAssurance(OFA)supportsGSFC'smissionswithsystemsreviewandprojectassurancemanagementresources.OFA'sOfficeofSystemReliabilityandSafety(SR&S)supportsGSFC'sprojectswithexpertiseintheareasofsafety,reliabilityandsoftwareassurance.SR&SalsohastheresponsibleforformulatingGSFC'smanagementpoliciesandestablishingminimumtechnicalrequirementsinthosethreeareas.TheSATCaidsSR&Sintheexecutionofitssoftwareassuranceresponsibilities.TheSATCassistsindividualflightprojectsandMODSDorganizationstoadaptanduseevolvingsoftwareassurancetechnologies.TheseorganizationsalsoprovidethedataformostoftheSATC'sresearchactivities,includingthedocumentsusedintheSATCSRSstudy.TheSATC'smissionistoassistNationalAeronauticsandSpaceAdministration(NASA)projectstoimprovethequalityofsoftwarethattheyacquireordevelop.TheSATC'seffortsarecurrentlyfocusedonthedevelopmentanduseofsoftwaremetricmethodologiesandtoolsthatidentifyandassessrisksassociatedwithperformanceandscheduleddelivery.Softwarestandards,guidebooks,toolsandtechnicalreports/papersproducedbytheSATCcanbeaccessedattheWebaddress;(1)definethecharacteristicsthatshouldbeexhibitedbyaSRS,(2)identifywhatcouldbemeasured,(3)developindicatorsofquality,(4)developatooltoperformthemeasurements,(5)analyzetheSRSdocumentsinlightofthereportsgeneratedbythetool,(6)identify