Figure2.1:ASimpleQueuingSystem
Inaqueuingsystemthereisworkthatarrivestoaprocessandthereisworkthat
departsaprocess.Whenmakingadeterminationofwhethersomethingcountsasin
progressornot,thefirstaspectofsystemthatneedstobeconsiderediswhatdoesitmean
forsomethingtohave“arrived”?Thatistosay,yourteamneedstodefineaspecificpoint
whereaunitofworktransformsfrombeingjustsomearbitraryideaintobeinga
legitimateworkitemthatistoimmediatelybeactedonandcompleted.Beforethatarrival
point,theitemisjustsomecandidateforwork.Afterthatarrivalpoint,theitemiscounted
asWorkInProgress.
Inapull-basedsystem,anentry(orboundary)pointisfairlyeasytodefine.Thatisbecauseinapullsystem,a
teamonlystartsworkwhenithascapacitytodoso.Thus,aworkitemcanonlycountasWorkInProgressifit
hasbeenvoluntarilypulledintotheprocessbytheindividual,team,ororganizationresponsibleforoperating
thatprocess.The“arrivalpoint”ofthesystem,therefore,isthepointatwhichtheteamperformsitsfirstpull
transactiononthework.Afterthatfirstpulltransaction,anitemisconsideredWIPuntilitdepartstheprocess.
(Thisarrivalpointisalsoconsideredapointof“commitment”.Anin-depthlookathowjust-in-time
commitmentandjust-in-timeprioritizationworkaretopicsthatIwillcoverinChapter8).
Forpush-basedsystems,anentrypointismuchhardertodefine.Thatisbecausethereisnoconsiderationfora
team’scapacitywhendecidingwhenworkshouldbestarted.Inapushsystemworkcanbeconsideredstarted
whenanystakeholderhasareasonableexpectationthatworkhasbeencommittedto(whethertheteam
responsibleforperformingtheworkknowsaboutitoragreestoitornot).Thisexpectationcouldbesetforsuch
arbitraryreasonsastheworkhasbeenrequested,theprojecthasbeenfunded,orsomemanagersomewhere
thinksitisagoodideatostart—regardlessofwhetherthereisanycapacitytodoso.
ObviouslyIhaveabiasforpullsystemsoverpushsystems,buttheconceptofWIPappliesregardlessofcontext.
Ifyoufindyourselfoperatingwithinapushsystem,thenthebest,firstpredictabilityexerciseyoumightwantto
undertakeistodefinetheboundariesaroundyourprocess.GettingahandleonwhatyouconsiderWIPisa
necessary(butunfortunatelynotsufficient)stepdowntheroadtopredictability.
Foraworkitemtonolongercountasinprogress,theremustbeaspecificpointof
departurefromtheprocess.Departurecouldbedefinedasdeliverytoanactualenduseror
deliverytosomeotherdownstreamteamorprocess.Forexample,ifadevelopmentteam
isresponsibleforitsowndeploymentstoproduction,thenthatteammightconsideran
itemonlytohavedepartedonceadeploymenttoproductionhasbeenmade.Oradifferent
teamwhoisnotresponsiblefordeploymentsmightconsideranitemtoonlyhavedeparted
onceithasbeenreasonablyhandedofftoadownstreamoperationsteamwhowouldthen
handledeployments.Again,thedefinitionofapointofdepartureholdstruewhetheryou
areoperatingapullorapushsystem.
Tosumup,forinprogressdefinitionpurposesyourteammustaspecificpointwhen
itconsidersworktohavearrivedtotheprocessanditmustdefineaspecificpointwhere
workhasdepartedtheprocess.Thedefinitionofthosetwosystemboundariesisthe
crucialstartingpointinpredictableprocessdesign.Onceyouhavemadethosedecisions,
thenallworkitemsbetweenthosetwopointswillcountasWorkInProgress:
WIP:Alldiscreteunitsofcustomervaluethathaveenteredagivenprocessbuthavenotexited.
IfdefiningWIPisthehardpart,thenmeasuringitistheeasypart.TocalculateWIP
yousimplycountthediscretenumberofworkitemswithinyourprocessboundariesas