Operational Research, Econometrics, and Software Engineering 1 Keep it Descriptive Stupid!

  • 格式:pdf
  • 大小:55.50 KB
  • 文档页数:3

KindredKIDS:KeepingitDescriptivein

OperationalResearch,Econometrics,and

SoftwareEngineering

MatthijsdenBesten

23rdNovember2004

1KeepitDescriptiveStupid!

Multi–agentbasedsimulation(MABS)isbecomingincreasinglydescriptive.According

toEdmondsandMoss(2004,§2)thisisonlynaturalasMABS“allowsandfacilitates

amoredirectcorrespondencebetweenwhatisobservedandwhatismodelled.”But

shouldMABS’naturaltendenciesbecheeredorbooed?

ProponentsofMABSmightarguethatthehighlevelofdescriptivenessinMABS

reflectsthevirtuousfeaturesoftheapproach.Butwhatifthehighlevelofdescriptive-

nessandcorrespondinglackofsimplicityisratherasymptomofflawedandamateurish

research?Alsomodelsthatarenotbasedonmultipleagentscanbemoreorlessdescrip-

tive.Infieldsasfarapartasoperationalresearch,econometrics,andsoftwareengineering

agreatdealhasbeenwrittenonmodelconstructionandspecificationanditwouldbe

interestingtoseewhetherthisliteraturewouldratherplaceacolonoracommabetween

“keepitdescriptive”and“stupid”.

2KIDSinOperationalResearch

“Keepthemodelsimple”isstilltheoverarchingadviceinoperationalresearch(Robin-

son2004,§5.4.2).Despitethis,alsoinoperationalresearchthesizeandcomplexityof

modelsisgrowingmoreandmore.Chwif,BarrettoandPaul(2000,§3)identifyseveral

technicalandnon-technicalreasonsforthisdevelopment.Onthenon-technicalside,

thereisa“showoff”factorinthatmanagersmightbemoreimpressedwithcomplex

modelswithagreatdealofanimation;thereisan“includeall”syndromeinthatinex-

periencedmodellersmightfeelinsecureaboutexcludinganythingfromthesimulation

model;andthereisa“possibility”factorinthatsoftwaretoolsandcomputermakethat

complexityandsizedonotconstraintmodelbuildinganymore.Onthetechnicalside,

thereisalackofunderstandingoftherealsystem;thereisaninabilitytomodelthe

problemcorrectly;thereisaninabilitytotranslateorcodetheconceptualmodelinto

1acomputerisedmodel;orthereislackofclearsimulationobjectivesthatmightinhibit

theconstructionofsimplemodels.Onthewhole,theoperationalresearchcommunity

recognisesthatover–simplifiedmodelsmightbelessvalid,morelimitedinscope,and

moredifficulttounderstandthanmoredescriptiveanddetailedmodels,butthisisre-

gardedasasmallpricetopaysincesimplemodelsareeasiertoimplement,validate,

andanalyse,areeasiertochange,andrequirelesstimetoinvestigate(Chwifetal.

2000,§5).What’smorethecommunity’sverdictisbackedupbyextensiveexperience

(RobinsonandPidd1998,Tilanus1985).Constructivelysimplemodels“encouragean

evolutionaryapproach;encouragethedevelopmentofaseriesofsmallmodels;reduce

theneedforon-goingassistance;aremorecloselytailoredtoclientcapabilities;facilitate

obtainingmanagementsupport;facilitateuser-participation;[and]facilitatesellingthe

system”(Ward1989).Yet,sometimesmoredetailanddescriptioncanbegoodwhenthe

sacrificeofsimplicitymakesthemodelmoretransparenttotheclientsandparticipants

(Ward1989).

3KIDSinEconometrics

Itusedtobethecasethateconometricianscontendedthemselveswithestimatingthe

parametersofamodelprovidedbyeconomictheory,butsincethemid-1970sadebate

hasbeenragingabouthowmodelsshouldbespecified.Thedebatespurnedanumber

ofgeneralprinciples(Kennedy2000,§5.3):

•Theoryshouldbethefoundationandguidingforceinaspecificationsearch;

•“Testingdown”ismoresuitablethan“testingup”;oneshouldbeginwithagen-

eral,unrestrictedmodelandthensystematicallysimplifyitinlightofthesample

evidence;

•Modelsshouldroutinelybeexposedtoabatteryofmisspecificationdiagnostictests

beforebeingaccepted;

•Researchersshouldbeobligedtoshowtotheirmodelencompassesrivalmodels;

•Boundsontherangeofresultscorrespondingtodifferentreasonablespecifications

shouldbereported,ratherthanjustprovidingtheresultsofthespecificationeven-

tuallyadopted,andthepathtakentotheselectionofthisspecificationshouldbe

fullyreported.

Althoughthesegeneralprinciplesapplyspecificallytoeconometricswhereitisrelatively

easytogeneratealternativemodelsthatarenotdifficulttovalidate,onecouldseehow

similarprinciplescouldguideMABSaswell.Andtheprinciplesaremorecongruent

withkeepingitdescriptivethanwithkeepingitsimple.

24KIDSinSoftwareEngineering

EdmondsandMoss(2004,§1)acknowledgethat“‘KeepitSimpleStupid”makesgood

senseifyouaredesigningorconstructingsomething’.Nonetheless,eveninsoftware

engineering,thereisatendencytovaluedescriptivenessoversimplicity.Thistendency

isalsoknownas“featurecreep”.Thatis,theproblemsthatsoftwaredevelopersfaceare

notfundamentallydifferentfromtheproblemsfacedbymodellersandhencemodellers

mightbenefitfromtoolsthathavebeendevelopedtoaidsoftwaredevelopment.Morein

particular,theunifiedmodellinglanguagemightbeemployedtomakethemodeltrans-

parenttoclientsandparticipants,versioncontrolsystemsmightbeemployedtokeep

trackofthemodeldevelopment,andsoftwareengineeringmetricsmightbeemployedto

keeptrackofthemodelbuildingexpenditure.

5KeepitDescriptiveStupid?