系统工程第三章

Chapter3FormulationofIssues 上午5时41分 2007SYSTEMSENGINEERING 2 1INTRODUCTION Itisveryimportant webelieve thattextsonsystemsengineeringandproblemsolving ingeneral paysignificantattentiontoissueformulation asastepinsystemsengineeringthatneedstooccurineachofthephasesofeffort Thisissobecause inpractice theresultsofapoorissueformulationeffortmaybesubjecttoverydetailedanalysis andtheresultsofthisarecarriedoverintoimplementation Asaresult weobtainthewrongsystem Needlesstosay thisusuallyresultsinawasteofresourcesand throughengineering aninferiorsystem comparedtothatwhichmighthaveresultedfromabetterissueformulation Issueformulationiscriticalacrossthedefinition development anddeploymentphasesofasystemsengineeringlifecycle Thisisnotastepimplementedonlyaspartofthesystemsdefinitionphase althoughitisveryimportantinthatphase 上午5时41分 2007SYSTEMSENGINEERING 3 1INTRODUCTION Aproblem oranissueasagenerallysynonymousterm canusuallybeviewedfromseveralperspectives andthesolutionthatresultswilloftenbeastrongfunctionoftheperspectivesfromwhichaproblemisviewedandformulated 上午5时41分 2007SYSTEMSENGINEERING 4 1INTRODUCTION Issueformulationbeginswithadefinitionoftheproblemorissuetoberesolved Thisincludesanassessmentofthesituationsurroundingtheproblem Situationassessmentisimportantinproblemsolvingandissueresolution Therearemanyaspectsoftheenvironmentsurroundinganissuethatweneedtoknowaboutinordertobeabletogeneratepotentiallyfeasiblealternativecoursesofactionthatcanleadtoissueresolution Manyofthesefactorsaredynamic uncertain andsubjecttochangewiththepassageoftime Situationassessmentmeansthatweneedtomakeacarefulappraisalofthevariousfactorsthatinfluenceaparticularobservedstateorcondition Generatinggoodalternatives onesthattrulysatisfytheneedsofourcustomersinaneffective efficient equitable andexplicablemanner dependsonanindepthsituationassessment 上午5时41分 2007SYSTEMSENGINEERING 5 2SITUATIONASSESSMENT CompletesituationassessmentconsistsofthreebasicstepsthatareintendedtoanswerthethreequestionshighlightedinFigure3 1 上午5时41分 2007SYSTEMSENGINEERING 6 2SITUATIONASSESSMENT Thefirstpartistheidentificationofthe immediate pastintermsofthequestion Whatwas Thesecondpartofasituationassessmentexaminesthecurrentstatusorpositionofthingsrelativetothegoal Itisadescriptivecomponentandanswersthequestion Whatis Thethirdornormativecomponentofasituationassessmentanswersthequestion Whatoughttobe Understandingofthemajor ideallyall factorsinfluencingthepast present andfutureisneededforagoodsituationassessment Thereisahorizoncomponentofsituationassessmentanditanswersthequestion Whatfactorsovertimematterandwhendotheymatter 上午5时41分 2007SYSTEMSENGINEERING 7 2SITUATIONASSESSMENT Wehaveacompletesituationassessmentonceweknowthefollowing Whatdowewanttoaccomplish Whatisthepastandcurrentstateofaffairsrelativetoourgoalbroughtaboutbythechangedsituation Whataretherelevantfactorsthatinfluencethesituationandtheirassociatedtimeframe 上午5时41分 2007SYSTEMSENGINEERING 8 2SITUATIONASSESSMENT Therearealargevarietyofenvironmentsinwhichvarioussystemsmustoperate Anumberofdifferentperspectives suchastechnical economic legal political cultural andsocial canbeimportantforunderstandingasystem senvironment Whenanadequateappreciationofalltheimportantperspectivesisachieved thenwesaywehavepreservedthecontextualintegrityoftheissuesunderconsideration Theproblemofissuedefinition andtheresultingidentificationofworthwhilealternatives dependsonanaccurateandtimelysituationassessmentthatpreservesthiscontextualintegrity 上午5时41分 2007SYSTEMSENGINEERING 9 2SITUATIONASSESSMENT Accomplishingahigh qualitysituationassessmentdependsonseveralfactors First theexperientialfamiliaritywiththeissuesorproblemunderconsiderationisveryimportant Forexample itisunlikelythatsomeonewithverylittlebackgroundknowledgeaboutnuclearpowerplantswouldbeable withoutconsiderablestudy todevelopusefulalternativesforensuringsafeoperationofsuchafacility Aswehavealreadynoted knowledgeisinformationinarelevantcontext 上午5时41分 2007SYSTEMSENGINEERING 10 2SITUATIONASSESSMENT Butyouneedmorethanjustknowledgeaboutthespecificproblemorissueathand Familiaritywiththeenvironmentintowhichthespecificissueorproblemisembeddedisalsocrucialtoanunderstandingofcontext Forexample thedesignofasuccessfulinformationsystemforairlinereservationagentsismademucheasierbysomeonewithanindepthknowledgeofthevarioustasksthatsuchagentsperformandtheenvironmentthatagentsmustcopewithastheyperformthesetasks Youcouldlearnalotaboutdesigningsuchasystemfromsomeonewhoisanexpertatdevelopinghuman computerinterfaces Butyoucanalsoappreciatehowhelpfulitwouldbetointerviewsomeexperiencedticketagentsandtofindoutaboutthedifficultiestheyexperiencewhentalkingtocustomersandbookingtheirflights Itisthejobofsystemsengineerstomakesurethattherelevantknowledgeofexperiencedpeopleisbroughtintoaprojectandusedinissueformulation Capturingthisknowledgeoftenrequiresthesystemsengineertoskillfullyconductbothindividualinterviewsandgroupmeetings 上午5时41分 2007SYSTEMSENGINEERING 11 2SITUATIONASSESSMENT Anormativescenariodescribeshowthestakeholderswantthesystemtobeinthefuture Thisisnotaseasytoaccomplishasitmightappeartobe Wewilloftenneedtodistinguishbetweenrealisticneedsandfrivolouswants Oftenalso importantstakeholdershaveconflictingopinionsonwhatthefutureshouldbe oronb Somehaveunrealisticexpectationsofwhattechnologycandeliverinthetimeframe 期限 underconsideration Othersarereluctanttoseeanychangesbecausetheythinktheirjoborrelationshiptoasystemmaybeputinjeopardy 危险 Askilledsystemsengineermustbrokerthesevariousintereststocreateenthusiasmandsupportforatechnicallyfeasible trustworthyproject Onewayofgainingsupportforanimprovementtoanexistingsystemorforacompletelynewsystemistoinvolvestakeholdersintheprocess Helpingpeoplevisualizethefutureinmeaningfulwayswillgoalongwaytowardcreatingausefulnormativescenario 上午5时41分 2007SYSTEMSENGINEERING 12 2SITUATIONASSESSMENT Buthowcanyouseeintothefuture Besidestalkingtokeypeople anotherwayofaccomplishingasituationassessmentistoobservethecurrentsystem ifoneexists Anobjectiveappraisaloftheproblemswiththecurrentsystemcanbeveryhelpful Asimplelistingoftheseobservationsinalogbookbydateandtimeisoftenworthwhile Besuretonotethemainideasofpeoplemanagingandworkingwiththesystem Often problemswillnotbeevidentonthefirstvisit Subsequentvisitswillrevealmore Peoplealsoaremoreopenwithyouaftertheygettoknowyouandfeelcomfortablewithyou Informationgainedbyobservingthecurrentsystemandtalkingtopeopleinvolvedwithitismostvaluableforwritingadescriptivescenario Adescriptivescenariotellswhythecurrentsystemcameintobeing howitworks andwhatproblemsareassociatedwithit Youshouldincludethemainactorsorstakeholdersinvolvedwiththecurrentsysteminyourdescriptivescenario Thesestakeholderswillusuallybeowners users customers clients managers maintainers administrators andregulatorsofthecurrentsystem But foracompletesituationassessmentyouwillalsoneedanormativescenario 上午5时41分 2007SYSTEMSENGINEERING 13 2SITUATIONASSESSMENT Ifthereisnotacurrentsystemtoobserve thenyouneedtocreateawayofseeinghowanentirelynewsystemmightwork Anumberofusefulwaysexistforthis Agroupofpeoplewithrelevantknowledgecanmeetandtalkthroughhowanewsystemmightwork 上午5时41分 2007SYSTEMSENGINEERING 14 2SITUATIONASSESSMENT Manyotherwaysexistforexaminingpossibilitiesfornewsystems Prototypes 3 4 canbebuiltandpotentialuserscanexperimentwiththemthroughsimulation Aprototypeisafirst cutapproximationofwhatanewsystemmightbe Thepurposeofaprototypeistoquicklygaininformationfromtheuseraboutwhatseemstoworkandwhatisneeded Forexample aprototypeofanewinformationsystemmightbeasetofscreensthatausercouldviewandcommentastohowusefulthescreensareinhelpingprovideneededinformation 上午5时41分 2007SYSTEMSENGINEERING 15 2SITUATIONASSESSMENT Amodelofthesituation andtheresultingsimulationofoperationsusingthemodel canemulatetheoperationofanewsystem Tobuildasimulationrequiresamodelorsomerepresentationofthenewsystem Theusualpurposeofasimulationistogetanideaofhowthenewsystemmightactuallyworkifitwereputintooperation Forexample acitywantingtobuildanairportatanewlocationmightliketoknowifthelandavailablecanaccommodatethenumberofplanesthattheyanticipatewillbelandingandtaking offfromtheirnewfacility Asimulationofanairportthatfitswithinthecity slandconstraintcanbetestedtoseeifanyairportlayoutscansuccessfullymeetanticipatedpassengerandfreightdemands 上午5时41分 2007SYSTEMSENGINEERING 16 3APPROACHESTOSITUATIONASSESSMENT Noblesaysthatsituationassessmentincludesthefollowing AnestimateofthepurposeofactivitiesintheobservedsituationAnunderstandingoftherolesoftheparticipantsintheseactivitiesInferencesaboutcompletedorongoingactivitiesthatcannotbedirectlyobservedInferencesaboutfutureactivities 上午5时41分 2007SYSTEMSENGINEERING 17 3APPROACHESTOSITUATIONASSESSMENT Thenotionofathresholdisoftenveryimportantinsituationassessment Wemighthaveathresholdforasituation andobservingthisthresholdmightbeallthatisrequired Whenthesituationdescriptorvaluesexceedthisthreshold wemightthendecidetoassessitingreaterdetail Ifitisbenign wemaychoosetoignoreit ifitisnotbenign wemaydecidetoreacttoitorcontinuetoobserveit Areasonablygoodillustrationofthisisthesituationassessmentoftemperatureofthehumanbody Oneofthepotentialdifficultiesrelativetoobservingasituationisthatwewishtobeabletointeractivelyandproactivelydealwithissuesandnotsimplytoreacttodifficultiesaftertheyhaveeventuated 上午5时41分 2007SYSTEMSENGINEERING 18 3APPROACHESTOSITUATIONASSESSMENT Thegeneralsituationassessmentprocess illustratedinFigure3 2 bedescribedbythefollowingeightsteps Wemakegeneralobservationsofasmanypertinent 有关的 aspectsofthesituationaroundusasispossibleinordertoidentifyorconfirmthedescriptivescenarioorstatusquo 现状 Weseeifthisinformationindicatesachangeinthecurrentsituation Ifthereisnochange wegobacktostep1 Ifthereisachange weproceedtostep3 Weidentifyorformulateanumberofalternativehypothesesthatmaydescribethenewsituation ordescriptivescenario Weattempttodetermineifanymoreinformationinputsarerequiredfordecidingwhichalternativehypothesisisthemostlikelyone 上午5时41分 2007SYSTEMSENGINEERING 19 3APPROACHESTOSITUATIONASSESSMENT Weobtaintherequiredinformationfromsuchinputsourcesasaprioripredefinedstoredinformation humanobservations humanknowledge orsensormeasurements Weprocessthisinformationandknowledgetoconfirmordisconfirmeachofthealternativehypotheses Weidentifythehypotheseswiththehighestprobability ies ofbeingtrueandidentifytheassociatedsituationassessmentwithsomeappropriatequantificationofourconfidenceintheassessment Wedetermineiftheassessmentconfidencefordescribingthesituationissufficientlyhigh Ifitisnot wegobacktostep3or4andrepeattheassessmentprocessuntiltheconfidencethresholdisachieved Whenitis wehaveassessedthesituationandwegoonwiththerestoftheproblem solvingorissueformulationprocess 上午5时41分 2007SYSTEMSENGINEERING 20 3APPROACHESTOSITUATIONASSESSMENT 上午5时41分 2007SYSTEMSENGINEERING 21 3APPROACHESTOSITUATIONASSESSMENT Oneofthemostdifficultproblemsincomplexdecisionsituationsisgatheringtheappropriateinformationandproperlyassessingthesituation MasonandMitroffareamongthemanywhohavecommentedonthisreality Theseauthorsidentifythreetypesoferrorsthatcanoccurinassessingasituation TypeIerrorsareerrorsthatresultfromincorrectlyassessingthatthereisaproblemwhenthereisnoproblem TypeIIerrorsareerrorsthatresultfromincorrectlyassessingthatthereisnoproblemwhenthereisaproblem TypeIIIerrorsareerrorsthatresultfromcorrectlyassessingthatthereisaproblem butincorrectlyidentifyingthenatureoftheproblem 上午5时41分 2007SYSTEMSENGINEERING 22 3APPROACHESTOSITUATIONASSESSMENT TypeIerrorsaregenerallycalledfalsealarms TypeIIerrorsarecalledmissesormissedproblemerrors TypeIIIerrorscannotgenerallybeovercomebyeventhebestmethodsofproblemsolvingbecauseoneissolvingtheincorrectproblem Onlybysomerarefortuitous 幸运 circumstancewouldoneeverendupwithanappropriatesolutionfortherealproblemathandaftermisdiagnosisandimplementingacourseofactionforthewrongproblem AmajorreasonforsituationassessmentistoavoidTypeIIIerrors 上午5时41分 2007SYSTEMSENGINEERING 23 3APPROACHESTOSITUATIONASSESSMENT TypeIIIerrorsoccurmostfrequentlywhenproblemsareill structured Inthiscontext itislikelythatthemostdifficultstepinthedecisionprocesswouldbetheproblemdefinitionorsituationassessment ComplexproblemsarethoseproblemsthatrequiremultidisciplinaryperspectivesifTypeIIIerrorsaretobeminimized Aproblemisill structuredwhenoneormoreofthedecisionalternatives decisionoutcomes valuesorweightsofimportanceoftheoutcomes ortheprobabilitiesofthevariousoutcomesthatresultfromimplementingvariousalternativecoursesofactionareeitherunknown impreciselyknown oruncertain 上午5时41分 2007SYSTEMSENGINEERING 24 3APPROACHESTOSITUATIONASSESSMENT Briefly anill structuredproblemisoneinwhichitisdifficult ifnotimpossible toreachaconsensus 一致同意 regardingthebasicdefinitionoftheproblemanditspossiblesolutions Virtuallyallreal worldproblemsareill structured anditistheseproblemsforwhichstructuredsituationassessmentaidsaremostneeded Wehaveoutlinedsomeoftheconsiderationsthatneedtobegiventoestablishingsituationassessmentaidsfortheseproblems 上午5时41分 2007SYSTEMSENGINEERING 25 4PROBLEMORISSUEIDENTIFICATION Thetoughestpartofmostsystemsengineeringeffortsisidentifyingtheproblemcorrectly Manyengineeringefforts althoughtheymayrepresentgreatfeatsofengineeringskill failbecausetheyweredesignedtosolvethewrongproblemorbecausetheimplementedsolutioncreatedmoreproblems 上午5时41分 2007SYSTEMSENGINEERING 26 3PROBLEMORISSUEIDENTIFICATION Forexample considertheAswanDaminEgyptbuiltinthe1960s HundredsoftheSovietengineerssetaboutandsuccessfullybuiltoneofthebiggestdamsandhydroelectricalfacilitiesintheworld However astheEgyptianssoonfoundout theeffortwas inmanyrespects agrandfailurebecauseitdestroyedmuchoftheprecious 宝贵的 arable 可耕种的 landintheNileRiverValley TheNileRiver snaturalfloodingprocesshadcontinuallyreplenished thesoildownstreamandmadeitpossibleformanycropstogrowinfertileriver bottomland Oncethedamwasinplace thenaturalfloodsnolongerreplenishedthelandandvastamountsofformerlyrichagriculturallandwaslostforever Egypt whichhadbeenabletofeeditself soonbecamedependentonfoodexports Furthermore thedamfloodedforevermanypricelessancientruinsunderdeepwaterthatwereupstreamfromthemassivedam 上午5时41分 2007SYSTEMSENGINEERING 27 4PROBLEMORISSUEIDENTIFICATION Whydidn ttheengineersconsidertheupstreamanddownstreamimpactsoftheproject Wecanguessthatthenarrowperspectivetakenbytheengineersledthemtoconcludethattheproblemwastoblocktremendousamountsofwaterbehindadamforgeneratingelectricityandpreventingfloods Thisledtothe solution ofoneproblemandthecreationofmoresignificantproblems Abroaderperspectiveoftheproblemwouldhaveaccountedfortheupstreamancientruinsandthedownstreamarablelandsand potentially avertedthistravesty Asystemsengineermustalwaysconsiderthepotentialnewproblemsorramificationscausedbyanyproposedsolutiontotheoriginalproblem 上午5时41分 2007SYSTEMSENGINEERING 28 4PROBLEMORISSUEIDENTIFICATION AstheAswanDamcaseshows identifyingaproblemorissueforalarge scaleprojectisnoteasybecausethereisnotjustonesimplequestiontosolveordifficultytoresolve Thelarge scaleprojectsthatsystemsengineersworkonrequiretheidentificationofmultiplequestionsordifficultiesthatmustbeansweredorresolved Andthereisnotasinglecorrectanswer Instead thereareusuallyanumberofalternativesthatcanbedeviseddependingonwhichdifficultiesthestakeholdersbelievetobemostimportant 上午5时41分 2007SYSTEMSENGINEERING 29 4 1ScopingandBoundingtheProblem howcanyousuccessfullyidentifytherelevantquestionsanddifficultiesinalarge scaleproject Properlyscopingandboundingasystemsengineeringeffortistheanswer Toscopeaprojectmeanstounderstandwhytheprojectisnecessary whatthestakeholdersintendtoaccomplishwiththeproject andhowtomeasureprojectsuccess Insystemsterms thismeansidentifyingtheneeds objectives andcriteriafortheproject Theneedstellwhytheprojectisnecessary Relatedtotheneeds theobjectivesdescribeindetaileverythingthattheprojectisintendedtoaccomplish Criteriameasuresuccessinachievingtheobjectives 上午5时41分 2007SYSTEMSENGINEERING 30 4 1ScopingandBoundingtheProblem Toboundaprojectmeanstounderstandthelimitationsassociatedwiththeproject thechangesthatcanbemadetoachievedesiredobjectives andtheimportantquantitiesthatarelikelytochangeasaresultoftheproject Insystemsterms thismeansidentifyingtheconstraints parameters andvariablesfortheproject Constraintsarethelimitsthatmustbeobservedfortheproject Constraintsincluderealisticconsiderationsrelatedtothingssuchasmoney time people organizations andsociety Forexample mostprojectshavebudget timedeadlines andenvironmentalimpactconstraints 上午5时41分 2007SYSTEMSENGINEERING 31 4 1ScopingandBoundingtheProblem Parametersarefactorsthatdefineanalternativeanddetermineitsbehavior Thevaluetowhichparametersaresetrestrictwhatresultsarepossibletoachievewithanalternative Forexample inthedesignofamasstransitsystemforacity someparametersmightbethenumberofbusesandtrains Howmanypeoplecanbemovedbyanyspecificmasstransitalternativedependsonthevaluetowhichtheseparametersareset howmanybusesandtrainsthereareforanalternative Onceasystemisinoperation parametersdonotchangemuch Everydaythatthecityoperatesthemasstransitsystem thesamenumberofbusesandtrainsarepartofthesystem Parametersarefactorsthatthesystemsengineermanipulatestocreatealternativesandaltertheirperformance Todistinguishparametersfromthequantitiesassociatedwithmathematicalmodels youcanrefertothemasalterables 上午5时41分 2007SYSTEMSENGINEERING 32 4 1ScopingandBoundingtheProblem Incontrasttoparameters responsevariablesarelikelytochangeoncethesystemisinoperation Variablesaremeasurablequantitiesthatyouwanttomonitorasthesystemoperates Forexample thenumberofpassengersthatusethebusesortrainseachdayisaresponsevariablethatchangesasthesystemoperates Forlarge scalesystemsthenumberofsuchvariablescanbeoverwhelming Thatiswhyweusetheconceptofstatevariables 上午5时41分 2007SYSTEMSENGINEERING 33 4 2SystemsDefinitionMatrix Statevariablesareacollectionofresponsevariablesthatwechoosetomonitortoinformusaboutthestatusofasystem Thespecificvariableschosendependonwhywewanttheinformation Ifwearesystemengineersinvestigatingtheadequacyofacurrentlyexistingmasstransitsys