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Quick Guide toDecision Modelingusing DMN 1.0

A White Paper February 2017, 2nd Edition

Gero Decker, Signavio, Inc.

Tom Debevoise, Signavio, Inc.

Page 2 of 22Quick Guide to Decision Modeling using DMN 1.0 – Signavio, Inc., April 2015

Table of Contents

1. WhyreadthisQuickGuide?...............................................................................................3

2. GettingStartedwithDMN1.0.............................................................................................4

3. DMNDiagrams:Focusingonthequestionstobeanswered....................................8

3.1FromProcessModelstoDecisionModels............................................................... 8

3.2Divide&Conquer...........................................................................................................9

3.3WhentodivideDecisionsintoSub-decisions........................................................10

3.4NamingConventionsforDecisions............................................................................11

3.5Inputs:SimpleTypesvs.ComplexObjects(BusinessObjects)..........................12

3.6WhentouseKnowledgeSources..............................................................................13

3.7WhentouseBusinessKnowledgeModels.............................................................13

4. WorkingwithDecisionTables...........................................................................................14

4.1CompleteorIncomplete?............................................................................................15

4.2ChoosingtherightHitPolicy.......................................................................................15

4.3FromDecisionTreestoDecisionTables..................................................................17

4.4FromCheckListstoDecisionTables:ThecaseofUniquevs.Anyvs.First.....18

4.5FromInputObjectstoInputExpressions..............................................................20

5. Conclusion.............................................................................................................................21

6. Contact..................................................................................................................................22

Page 3 of 22Quick Guide to Decision Modeling using DMN 1.0 – Signavio, Inc., April 2015

1. WhyreadthisQuickGuide?

TherearemanyreasonswhyBusinessDecisionManagement(BDM)shouldbehighonbusinessleader’sobjectives:

› Theavailabilityofbigdataandpowerfulanalyticstechnologythatuncoversnewopportunitiesfor“smarterdecisions”and

› ComplexrequirementsforcompliancerequireequallycomplexdecisionsthatarefulltraceablefrombusinessrequirementstoITimplementations.

Toreapthestrategicbenefitsofbigdataanalytics,businessesneedtoconnecttheoutputtotheoperationaldecisionsthatdriveprocesses.Tomaketheconnectionsbusinessesmusthaveadeepunderstandingofthesedecisionsandthelogicbehindthem,thedatathatdrivesthemandtheprocessestheydirect.BDMisanewdisciplinethatidentifiescataloguesandmodelsdecisions,partic-ularlyoperationaldecisions,intheenterprise.

Theobjectiveofadecisionmodelistocreateasharedunderstandingaboutitsdrivingfactors:thelogic,dataandprocesses.TherecentlyapprovedDecisionModelingandNotation(DMN)1.0standardfromtheObjectManagementGroup(OMG)isanotationthataccomplishesthesegoals.

DMN1.0helpsyouto

› discoverandoptimizeoperationaldecisionsinyourorganization

› documentbusinesslogicforregulatorycompliance

› designdecisionlogicforrules-centricautomationprojects

› driveperformanceusinganalytics

TheDMNstandardalsoprovidesapowerfulmeta-model,notationandsemanticsfordecisionmodeling.However,italsoofferslittleguidance.Likemoststandards,therearenobestpracticesorusagestyles.

ThisQuickGuideservesasanintroductiontodecisionmodelinginDMNfornovicemodelers.Itaimsforguidance,notforcompleteness.ItfocusesonfrequentlyaskedquestionsandoffersavarietyofpracticalrecommendationssothatyoucanimmediatelystartusingDMN. Happydecisionmodeling!

Page 4 of 22Quick Guide to Decision Modeling using DMN 1.0 – Signavio, Inc., April 2015

2.GettingStartedwithDMN1.0

DMNisacriticaladditionforthebusinessanalyststhatwishtomodelandimprovethedecisionsthattheirbusinessesmake.PriortotheDMNstandard,therewerenoopenstandardsformodeling thedataandlogicassociatedwiththeprocesses.Inthisquick-startguide,wewilllearnhowtomodeldecisionsbyimmediatelylookingatausecase:

Imagineyouareworkingatabank.Acustomermakesarequesttowithdraw$9,000fromhissavingsaccount.Canyouaccepthisrequest,processthetransactionandhandhimthemoney?

Youhavetomakeabusinessdecision.

Whatarethecriteriaforthecorrectdecisionandwhatinformationisyourchoicebasedon?Isitrelevantthatthecustomerhaswithdrawnalargesumlastweek?Isthereanupperbound?

Thebankhasstandardrulesforhandlingtherequest:

› Thereneedtobesufficientfundsintheaccount.

› Theidentityofthecustomerhastobeproperlyverified.Certaindocumentsmustbepresentfortransactionsgreaterthan$5,000.Moreover,whichtypeofdocumentisalloweddependsonthecustomer’snationality.

Yet,theserulesarejustaportionofthelogicneededtomakeadecisionaboutthewithdrawaloffunds.Businessesmakemanydifferentdecisionsthattakeplaceatthethreelevelsofbusiness:

› Strategic,thesedecisionshavelong-rangeimpacts.Theymightincludeenteringnewlinesofbusiness,acquisitionofcompaniesandassets

› Tactical,thesedecisionsinvolveexistinglinesofbusiness.Tacticaldecisionsincludego-to-marketplans,respondingtoimmediateopportunitiesandtakingadvantageofshort-termmarketadvan-tages.Tacticaldecisionsoccurmorefrequentlythanstrategicdecisions

› Operationaldecisions.Operationaldecisionsare‘baked’intoexistingbusinessprocessesandpractices.Operationaldecisionsoccurveryfrequently,sometimesscoresofthousandseachday.Examplesincludethepricesofitems,thediscountsoffered,andbasicbusinessdecisions.

Sothewithdrawaldecisionisasimpleexampleofanoperationaldecision.Itisconnectedtoaprocessthatvalidatesandtracksthewithdrawaloffundsfromcustomeraccounts.Basedoninputfacts,adecisionoutcomeisderived,leadingtoanactioninaprocess.Figure1presentsaDMNmodelofthisdecision.DMNisaninternationalstandardandversion1.0wasreleasedbyOMGinDec2014.

Page 5 of 22Quick Guide to Decision Modeling using DMN 1.0 – Signavio, Inc., April 2015

Figure1DMNdiagram

DMNdistinguishesbetweentwolevels:decisionrequirementsdiagrams(wewillsimplycallthemDMNdiagrams)anddecisionlogic.

Decisionsarerepresentedbyrectanglesandinputdatabyroundedrectangles.Inthisexample“Approvemoneywithdrawal”isthetop-leveldecision.“Sufficientfunds”and“Valididentification”aresubdecisions,theoutcomeofwhichisconsideredbytop-leveldecision.Theyarealsosubdecisionsbecausethequestionstheyposemustbeansweredbeforethemainquestion,“Approvemoneywithdrawal”,isanswered.Thearrowsdepictaflowofthedecisionsintothetop-leveldecision.Therecanalsobemorethanonetop-leveldecision.

Thirdelementtypes,calledknowledgesourceshelpusdepictdependenciesonpoliciesorregula-toryrequirements.Inthiscase,thelattertwosubdecisionsdependon“§154AO”,aparticularretailbankingregulation.

DMNdiagramsprovideahigh-leveloverviewofhowadecisiondependsonotherdecisions,policiesorregulationandinputdata.Decisionlogicspecifiesthedetailsofonedecision,sothatitcanbe easilyandunambiguouslyunderstoodbyahuman.Decisionmodelscanalsobeexecutableandincludedsystemcomponents.

Asshownintheprocessdiagrambelow,decisionscanbetightlyconnectedtobusinessprocesses.Operationaldecisionscanaffectaprocessinanumberofdistinctiveways.Decisionscandirectthenextsteporactivitytobetaken,whoisresponsiblefortheactivity,thecourseofactiontobetakenandthedatarequiredtocompletetheactionsofthedecision.

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Figure1a,thedecisioninfigure1controlsthisprocess.

DMNelement Description

Adecisionistheactofsettlingaquestionormakingadetermination,fromanumberofinputvalues,usinglogicdefininghowtheoutputisdeterminedfromtheinputs.

Decisionscandependonotherdecisions(subdecisions).

Decisionsdependoninputdatafordeterminingtheoutput.Wewillusetheterm“input objects”inthisdocument.

Knowledge sources areauthoritiesfordecisions.Often,itissourcedocuments,suchasinternalpoliciesorexternalregulationthatwereusedtoderivethedecis-ionlogic.

Information Requirementsshowtheneedinputofinformationfromeitherasub-decisionsorinputdata

Table1DMNelements

Page 7 of 22Quick Guide to Decision Modeling using DMN 1.0 – Signavio, Inc., April 2015

ADMNdiagramdoesnotdepictthedecisionlogicofaparticulardecision.Thisisdonethrougheitherlogicalexpressionsorthedecisiontablesthatareattachedtothedecision.Thedecisiontablefor“Approvemoneywithdrawal”isshowninfigure2.

Figure2Decisiontablefor“Approvemoneywithdrawal”

TheACcolumnorderstherulesinthetable.Undercertainconditions,thisorderisimportantfordeterminingwhichrule‘fires’.Thetwocolumnsontheleftaretheinputs.Thecolumnontherightistheoutputofthedecision.Eachrowisarule:Itshowswhichcombinationofinputvaluesleadstowhichoutputvalue.

Inthisexample,moneywithdrawalisonlyapprovediftherearesufficientfundsandthereisvalididentification.

Therulethatnoidentitydocumentisrequiredforwithdrawalsoflessthan$5,000ispartofthe“Valididentification”decision.Theemptycellsdenoteawildcardmatchforanyvaluethatisprovided.Thecorrespondingdecisiontableisshowninfigure3.

Figure3Decisiontablefor“Valididentification”

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3.DMNDiagrams:Focusingonthequestionstobeanswered

Everydecisionresolvesorsettlesaquestion.Let’sconsiderthemoneywithdrawalexampleagain.Here,thequestionis:Isthecustomerallowedtowithdrawtherequestedamountfromhissavingsaccount?Thetwopossibleanswersare:“Approved”and“Notapproved”.

QuestionsandanswersarenotgraphicallyshowninDMNdiagrams.Theyareattributesofdecisions.

3.1FromProcessModelstoDecisionModels

Businessprocessmodelsareagreatwaytoshowthedecisionresponse.Mostdecisionsrespondtoanddirectabusinessprocess.Hereisanotherexamplefromthefinancialsector:Whendevelopingabusinessprocess,theobjectivesofthestorywillsuggestthecorrectquestionforthedecisions.Considerthefollowingstory:

Whenaninvestmentadviserentersintobusinessorexpandshisoperations,hemustregisterwithdifferentauthorities.EspeciallylargeadvisersoftenregisterwiththeSecuritiesandExchangeCommission(SEC),whileothersonlyregisteronthestatelevelorevennotatall.

Figure4BPMNdiagram

Thelabelofthegatewaydirectlyreferstotheoutputofthedecision.Thebranchingconditionsattachedtothesequenceflowedgesdescribethefourpossibleanswers.

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Question:Wheremusttheadviserregister?

Processresponses(Answers):

› Statelaw

› Statelaw,SECpotential

› Nonerequired

Therefore,theprocessobjectivedeterminesthequestiontobeanswered.Iftheprocesswasstruc-tureddifferently,thequestionwouldhavelookeddifferent,too.Forinstance,alternativequestions couldhavebeen“DoIneedtoregister?”(Answer:Yes/No)or“WhichstatesdoIhavetoregisterwith?”(Answer:listofcorrespondingstates).

3.2Divide&Conquer

Alwaysfocusingonthequestionalsohelpstosubdividecomplexdecisionsintosubdecisions.Figure5showsaDMNdiagramfortheexample.

Figure5Masteringcomplexdecisionsthroughsubdecisions

ThequestionwhethertheAdviserActisapplicabletotheadviserhasalargeimpactontheregistra-tionrequirement:IftheadviserdoesnotqualifyaccordingtoSection202thennoregistration isrequiredatall.Therefore,“ApplicabilityofSection202(a)(11)AdviserAct”wasintroducedasasubdecision.

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Thesizecategoryoftheadvisoriscriticaltothetopdecision.Thesizeclassifiesthecategoryanddifferentrulesapplytotheadviser.Wheretheadviserhastoregisterissplitintothethreesubdecisions:

› “Registrationrequirement(smalladviser)”,

› “Registrationrequirement(medium-sizedadviser)”

› “Registrationrequirement(largeadviser)”.

Slicingupalargerscenariointosmallerpieces,whichcanthenbetreated(“managed”)individually,isacommonmodelingpatternthatisnotonlyfoundindecisionmodeling:Divide&conquer.

Youcanapplydivideandconquerwhenmovingfromthetop-leveldecisiontosubdecisions(verticaldivide&conquer).Agoodexampleisthesub-decision“ApplicabilityofSection202(a)(11)AdviserAct”.Divide&conquercanalsobeusedinsegmentation(horizontaldivide&conquer).Slicingupthedecisionaccordingtothesizeclassificationisanexample.

3.3WhentodivideDecisionsintoSub-decisions

Findingthecorrectlevelofabstractionisanimportantsuccessfactorineverymodelingendeavor.Thisisespeciallytruewhendecidingtouseone“bigger”DMNdecisionorratherseveral“small”DMN.

ConsidertheinvestmentadviserDMNdiagraminfigure5.Here,thedifferentdecisionsaresmallenoughtodefinethedecisionlogicatalatterpoint.Also,thedecisionsarebigenoughnottogetlostinhugediagrams,Herearesomehintsthatcanhelpyoudecidewhentosplitupdecisionsintosubdecisions:

Criterion Description

Necessity Subdecisionsareoftennecessitatedbytheobjectivesoftheto-leveldecision.IfIntheexample,differentsize-specificregistrationrequirementsneededtobedecidedbeforethetop-leveldecisioncouldbemade.Simplyput,mostbusi-nessdecisionsneedtheinputofsubdecisions.

Reusability Subdecisionscanbereusedindifferentdecisionmodelsanddifferentcontexts.

Forinstance,the“Investmentadvisersizeclassification”mightnotonlyberele-vantforthequestionregisteringanadviserbutalsoforothercontexts.

Complexity Onceadecisionhasmorethan7inputsand/orsubdecisions,thisisaclearsignthatthedecisionlogicwillmostlikelybeverycomplex.Theideaisthathumansarestillabletounderstandthedecisionlogic–andnotonlymachines.Sobettersplitaverycomplexdecisionintotwoormoredecisions.

Authority DMNKnowledgeSourcescanbeusedtodepictpoliciesorregulatoryrequi-rementsthatinfluence/guideadecision.Toshowthatpartofthedecisionmakingisbasedonaninternalpolicyandanotherdependsonsomeexternalregulation,couldbeagoodreasonforsplittingupthedecisionintotwodecis-ions.

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Decision maker Whoismakingthedecision?Isitapersonorisitamachine?Ifdifferentpeopleordifferentsystemsaremakingdifferentpartsofadecision,thenyoumightneedtosplitupthedecisionintodecisionsmadebyonemachineoroneroleonly.

“Decisionmaker”isanattributeofdecisionsinDMNdiagrams(nographicalrepresentation).

Decision owner Everydecisioncanhaveadecisionowner.Thisisthepersonresponsibleforthedecisionoutcome.Iftherearedifferentpartsofadecisionwhichdifferentowners,youmightwanttosplitthedecisionupaccordingtoownership boundaries.

“Decisionowner”isanattributeofdecisionsinDMNdiagrams(notgraphicalrepresentation).

Table2Criteriaforsplittingupdecisionsintosubdecisions

Recommendation:Decisionmodelingisaniterativeexercise.Inmanyprojects,therightlevelofgranularitycomesnaturally.Thekeycriterionofthemodelisclarity:shareyourdecisionmodelwitha

colleagueandobservewhetherhe/sheunderstandsit.

3.4NamingConventionsforDecisions

WorkingwithdecisionsandsubdecisionssuggestsaneedfornamingconventionsinDMN.Table2showsthemostpopularlabelingstylesfoundinDMNdiagrams.

Namingstyle Example Description

Activity style Determinewhereto register

ThedecisionhasthesamelabelasthecorrespondingBPMNtask.Theactofdecisionmakingmovesintothecenter. Thisisa“verbobject”style.Typicalverbsare“check”,“determine”or“calculate”,“select’,“choose’.

Output style Investmentadvisersizeclassification

Thedecisionhasthesamelabelliketheoutputvariableofthedecisionlogic.

Often,youcanfindwordslike“applicability”,“eligibility”,“score”or“ranking”aspartofthislabelingstyle.

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Question style Providesadvicetoregisteredinvestmentcompaniesonly

Thedecisionlabelequalsthequestionoratleastisanabbreviatedversionofthequestion.

Thislabelingstyleisoftenobservedwhenturningcomplex/rawinputdata(suchascustomerbaseinthisexample)intosomethingmeaningful.

Attention:Questionsareoftenverylongandthereforeleadtoverylongdecisionlabels.

Table3Labelingstylesfordecisions

Recommendation:Usetheactivitystyleforthetop-leveldecision,tohighlighttheconnectiontothesurroundingprocess.Usetheoutputstyleforallotherdecisions.Insomecases,thequestionstyleismoreintuitivethantheoutputstyle.

3.5Inputs:SimpleTypesvs.ComplexObjects(BusinessObjects)

OntheDMNdiagramlevel,themodelercanselectthelevelofgranularityofinputobjects.FromthegraphicalrepresentationintheDMNdiagram,wecannottellwhetheraninputobjectisacomplexobjectorasimpletype.

Intheexampleabove,“AUM”(whichistheabbreviationfor“AssetsunderManagement”)ismostlikely asimpletype,namelyaUSDamount.Thecaseof“Location”isnotsoeasy:Itcouldeitherbeasimpletype(e.g.oneoftheUSstates)oracomplexobjectconsistingofastructuredaddress,includingstreet name,zipcode,state,countryorevengeolocation.Somebusinessanalystscallthesebusinessobjects.

Eachcomplexobjecthasmultiplefields.Everyfieldinturncanbeacomplexobjectorasimpletype.Zipcodeandstateareexamplesforsimpletypefields.Geolocationisanexampleforacomplexobjectfield:Itconsistsofthelatitudeandlongitude.

Manytimes,thedecisionrequirementsmodelersmightlackdetailedunderstandingofthestructureofthedata.Therefore,theymightnotknowwhetheritisasimpletypeoracomplexobject.

Thisisnotaproblemwhendraftingthefirstversionofadecisionmodel.InearlyphasesofDMNdiagrammodeling,itismoreimportanttoidentifytherightquestionsandanswers(thedecisions)andtheirdependencies.

Whendefiningthedetaileddecisionlogic,anunderstandingoftheunderlyingdatamodelisrequired.Decisionmodelingshouldbeacollaborativeeffortbetweenrequirementsmodelers,peoplewithdeepunderstandingofthedatamodelandsubjectmatterexpertswhocanexplainintricatedetailsofthedecisionlogic.

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Someorganizationshaveacentraltaxonomyordatadictionary,whichcontainsthemostrelevantterms/objectsandtheirrelationships.Thisisvaluableinputfordecisionmodeling.Ifproperlydone, adatadictionaryacceleratestheselectionoftherightinputobjectsandmapshigh-levelconceptstotechnicalobjectsinlaterstages.

Recommendation: Buildingadecisionmodelisaniterativeprocess.Donotwaitfortoomanyprerequisites(e.g.propercentraltaxonomy)tostartmodeling.Ratheruseacollaborativeapproachthatinvolvestherightpeople.

3.6WhentouseKnowledgeSources

Manydecisionsaredrivenbyexternalregulationandinternalcompliancepolicies.Earlycollectionoftheregulatoryrequirementsanddependenciesonpoliciesearlyonhelpscreateameaningfuldecisionmodel.

Aquestionoftenaskedwhethertonametheentireregulation/policyortodirectlypointtoaspecificchapter/section/paragraphwithinsuchadocument.Organizationsfrequentlyconnecttheirdecisionslogicwiththeproperregulations.

Recommendation:Useknowledgesourcestolisttherelevantdependenciesoninternalpoliciesorexternalregulation.

3.7WhentouseBusinessKnowledgeModels

ReuseofdecisionsisoneofthestrengthsofDMN.ManyDMNdiagramscontainsubdecisionswhicharespecifiedinadifferentDMNdiagram.Thequestion/answersandthedependenciesonsubdecisions,knowledgesources,inputobjectsanddecisionlogicareinheritedfromtheotherDMNdiagram.

DMNoffersyetanotherreusabilitymechanism,whichwehavenottalkedaboutsofar.The“businessknowledgemodel”representsreusabledecisionlogic.

BusinessKnowledgeisusedwheretwodecisionssharethesamedecisionlogic,butdependondifferentsubdecisionsandondifferentinputobjects,i.e.differentvariables.Inthiscase,businessknowledge modelscanbeusedtocreateacentraldefinitionofthedecisionlogicwhichcanthenbe“invoked”by twodifferentdecisions.

Reusabledecisions(sameinputobjects,samedependencyonsubdecisions,samedecisionlogic)iscommon,reusabledecisionlogicwithdifferentinputobjects/subdecisionsisrare.Thedecisionlogicembeddedinadecisionmodelcanbereusableacrossmodels.AnalternatetotheBusinessKnowl-edgeistoconnecttotheembeddeddecisiontable.

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4.WorkingwithDecisionTables

Acolleagueofyourssendsyouanemailabouthowdiscountsarecalculatedforcustomers:

› Adultswhoarenotmarriedgeta10%discount.

› Ifyouaremarried,yougetatleasta20%discount.

› Ifyouhavekids,youevengeta30%discount.

Accordingtothisdescription,thedecisiondependsonthefollowinginputs:Age(adult/child),maritalstatus(married/notmarried),parentalstatus(kids/nokids).

DecisiontablesarethenotationofchoicetospecifydecisionlogicinDMN.Whendirectlytranslatingtherulesfromtheexample,Figure6showstheresultingdecisiontable.

Whenstartingtodevelopthe‘rules’orlogicforthesewordproblems,youshoulddiscernwhatinputswillsettlethequestionsposedbythedecision.Inthiscaseourquestionis‘Whatdiscountshould wegivetoourcustomer’.Inourassignmentofoutput,wecanseethatitshouldbepossibletocreatearuleforeachcombinationoftheinputs.Inthisanalysiswedecideonthewaytherulesareevalu-atedinadecisiontable.Forinstance,theremightbearestrictionthatonlyonerowinthetablewillreturnanoutputresult.Thisisknownasa‘Uniquehit’policy.Thatsaid,theteamhasnotarticulatedalltherulecombinations.Asaruleanalyst,youhavetheoptionofexplicitlyaskingforthedesiredruleoutputforallthecombinations,oryoucanhavethecolleaguesdeveloptherules,basedonananalysisofthewrittenrequirements.Frequently,thelatteranalysisishoworganizationsdeveloptheirlogic.

Figure6Decisiontablewitherrors:incompletenessandoverlappingrules,thisisapartialeffort

Wherethereisnoentryinaninputcell,thereisanimplicit‘wildcard’thatmatchesanyvalue.Forinstance,rule2matchesanypersonwithamaritalstatusof“Married”.Thereareseveralerrorsoroverlapsinthisdecisionlogic.ThedecisionlogicverificationfunctionalityofSignavioidentifiesthefollowingproblems:

› Thefollowingcombinationsofinputvaluesarenotcoveredbyanyrule(Age=Child,Maritalstatus=Notmarried,Parentalstatus=Nokids)

› UniquehitpolicyviolatedforRule1and3,thesecombinationsofinputvaluesarecoveredbymorethanonerule:(Age=Adult,Maritalstatus=Notmarried,Parentalstatus=Kids)

› UniquehitpolicyviolatedforRule2and3,thesecombinationsofinputvaluesarecoveredbymorethanonerule:(Maritalstatus=Married,Parentalstatus=Kids)

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Becauseweareseekingtocreatea‘unique’policyfortherulesinthetables,thesestatementssuggestthisdecisiontableis“incomplete”(error1).Also,thereareinputcombinationsthatarecoveredbyseveralrulesinthedecisiontable(errors2and3).

Decisiontablesarenotrequiredtobecompleteorgapfree:Inadiscountcalculationexample,aninputvaluecombinationthatisnotcoveredbyanyrulecouldeasilybeinterpretedas“nodiscount”.Overlappingrulesarepermitted,iftheyallhavethesameoutput,orifthereisacertainpriorityconfiguredforwhichofthematchingrulesactuallyapplies.YoucanconfigureaDMNdecisiontableregardingcompletenessandhitpolicy.

ThehitpolicyinaDMNDecisionTablespecifieshowthetheresultofthedecisiontablewillbeevalu-atedwheretherearemultiplematchesforagivensetofinputs.Thehitpolicycontainsadditionalinformationthatcanbeusedtocheckcorrectnessofdecisiontableatdesign-time.

4.1CompleteorIncomplete?

Inourexample,thereisnoruleforchildrenwhoarenotmarriedandwhodonothavekids.AccordingtotheDMNstandard,thisisan“incomplete”decisiontable.Thesimpleresolutionforthisexamplewouldbetoaddanotherruleforexactlythiscase.Thiswouldturnitintoacompletedecisiontable.

Completenessisonlypossibleifthevaluedomainsforallinputsareknown.Inourexample,thisisthecase:eachinputhasavaluedomainconsistingoftwovalues.

Recommendation: Usecompletedecisiontables,wheneverpossible.Thisavoidsmisunderstandingsaboutthedecisionlogic.

4.2ChoosingtherightHitPolicy

Hitpoliciesandtheproblemwearesolvingdeterminethesemanticsofadecisiontable.Theyalsoimposerequirementsonhowrulesmustbestructured.Theconditionsofthebusinessrulesalsocandictatethehitpolicyandtheruleswithinthetable.

Hitpolicy Description Application

Unique (single) Onlyoneruleisallowedtofireforanyonecombi-nationofinputs.

Inthiscontext,allinputsareassumedtobeindepen-dentlypartitionedfromeachother,i.e.thatanycombinationisactuallypossible.Forourexample,itisassumedthatchildrencanalsobemarried.

OurexampledecisiontableviolatestheUniquerequirement,astherearerulesthatoverlap.

Unique(single)isthedefaultintheDMNstandard.

Whereauniformpolicyisrequiredforthecombinationofinputs

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Any (single) Multiplerulescoverthesamecombinationofinputvalues.However,thisoverlapisonlyallowediftheoverlappingruleshavethesameoutput.

Figure2showsavalidexampleofadecisiontablewithhitpolicyAny.

Adiagnosisofamedicalcon-ditionoftheortheoutputoflabresultsmightneedanAny’policyifvariousrangesofsimilardiagnostictestidentifythesamecondition

Priority (single) Rulescanoverlapwithdifferentoutputs.

Inordertodeterminetheresultingoutput,outputsareorderedaccordingtopriority(e.g.thehighestdiscountwins).

Priorityrulesresolve‘race’conditions,suchasevaluatingtheweightedscoresofvariouspriorities.

First (single) Rulesmightoverlap.Butonlyonerulefires:TheFirsthitpolicysimplyassumesanorderingoftherules–theyareevaluatedfromtoptobottom.Assoonasonerulefires,theoutputofthatruleisusedasresultofthedecision.Onceonerulehits,nootherruleischecked.

Wheninterpretingourexampledecisiontableusingthefirsthitsemantics,adultswhoarenotmarriedbuthavekids,wouldonlyget10%discount(insteadof30%).

No Order (multi)

Multiplerulescanfirewithoutanexplicitorder.Multihittableseitherreturnasetoraggregatethefinalresultsofthedecisions.DMN’sdefaultisprovidethesetofoutputvaluesasresult.Inourexamplethiswouldbe{10%,30%}fornotmarriedadultswithkids.Multi-ruletablecanapplyaggre-gationfunctionssuchasmin,max,avgtoderiveasinglevaluefromasetofoutputvalues.

Multihitpoliciesaregoodforscorecardsthataccumulateformatchinginputs.Forinstancetheconditionofaninspecteditemmightbebasedonmulti-plechecksandwithpointsoffforvariousdefects.

Table4themostrelevantDMNhitpolicies

Allofthesehitpolicies(exceptfortheFirsthitpolicy)aredeclarativeinnature,i.e.theorderingoftherulesdoesnothaveanysemantics.TheFirsthitpolicyisnotdeclarative,butprocedural.Thishit policymightbeusedbypeoplewithatechnicalbackground(whereifthenelsestatementsarealsoevaluatedinaparticularorder),butitiscountertothedeclarativenatureofDMN.

Recommendation: Ifyouareunsureofthehitpolicy,startwiththeUniquehitpolicy.Thisforces youtodefinerulesthatdonotoverlapeachother.Asshownabove,someapplicationsneedoverlap-pingandadditiverules.Makecertaintherulesspecifythedesiredresults.Insomecases,the“Any” hitpolicyleadstomorecompactandmoreeasilyunderstandabledecisiontables.Donotusethe“Firsthit”policyandtrytoavoidthePriorityhitpolicy.Multihitistypicallyonlynecessaryforcertainscoringandcalculationscenarios.

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4.3FromDecisionTreestoDecisionTables

Decisiontablesareequivalenttodecisiongraphs(andviceversa).Itisalmostascommontousedecisiontreestodescribingdecisionlogicasitistouseworkflowdiagrams.

Youreturntotheteamtodiscussyourfindingsregardingincompletenessandthemissingrules.Obviously,therehasbeensomemisunderstanding.Toresolvethis,yourcolleaguedrawsasmallflowcharttoclarifythesemanticsofthediscountcalculation.

Figure7:BPMNdiagramusedasdecisiontree

BPMNwasusedtodrawthisdecisiontree.BPMNisnotmeanttobeusedformodelingdecisionlogic.AnupcomingversionofDMNwillmostlikelyincludegraphicaldecisiontreesasanalternativenotationofdecisionlogic.

Decisiontreescanveryeasilybetranslatedintodecisiontables.Eachdecisionnodefromadecisiontreeistranslatedintoacolumninthedecisiontable.Then,thetableisfilledfromlefttoright.

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Figure8Decisiontable(Unique,complete)derivedfromdecisiontree

Whenadecisiontreeistranslatedintoadecisiontable,theresultingdecisiontableautomaticallyfulfillstheUniquenessrequirement.Thecompletenessrequirementisalsofulfilledifeachdecisionnodesofthetreecoversthecompletevaluedomainofthecorrespondinginput.

Recommendation: DonotencodedecisionlogicinBPMNdiagrams.UseDMNdecisiontablesinstead.

4.4FromCheckListstoDecisionTables:ThecaseofUniquevs.Anyvs.First

Let’sassumethatapurchaseordercanbeacceptedif

› avalidquotationnumberisreferenced,

› thepricingmatchesthequote,

› allrequireditemsareincludedintheorder,and

› thequotationhasnotexpiredyet.

Thedecisionlogicbehindthischecklistis:Ifallconditionsaremet,thenthepurchaseorderis“acceptable”.Ifatleastoneconditionisnotmet,thepurchaseorderis“notacceptable”.

Translatingthisexampleusingfirsthitsemanticsleadstothedecisiontableinfigure9.

Figure9Firsthitdecisiontablederivedfromchecklist

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ThisexamplecaneasilybetranslatedintoanAnyhitdecisiontableandaUniquehitdecisiontable,whichisillustratedinfigures10and11.

Figure10Anyhitdecisiontablederivedfromchecklist

Figure11Uniquehitdecisiontablederivedfromchecklist

ThebigdifferencebetweentheFirsthittableandtheothertwoisthattheFirsthittableisconsider-ablysmaller.Thesecondrulefiresforallinputcombinations,servingasa“catchall”rule.

TheAnyhittablehasoneruleforeveryinput,coveringallnegativecasesforthatinput.

TheUniquehittablehasastructurelikeifitwasderivedfromadecisiontree(seeabove).Therequire-mentthattherulesmustnotoverlap,makesthedecisiontableappearmorecomplicatedthantheAnyhitdecisiontable.

Ingeneral,decisiontablesarenotthemostintuitivewayofrepresentingasimplechecklist.Decisiontablesarethebusinessuser-friendlyoptionwehaveinDMN.

Recommendation:Use“Any”hittablestorepresentchecklist-likescenarios.

Page 20 of 22Quick Guide to Decision Modeling using DMN 1.0 – Signavio, Inc., April 2015

4.5FromInputObjectstoInputExpressions

Intheprevioussectionwehavebrieflytouchedonthequestionofsimpletypesvs.complexobjects.WhenrelatingDMNdiagramstodecisiontables,thisisoneofthecentralquestions.

Inputstodecisiontablesmustalwaysbeasimpletype.Table5showsalistoftypicalexamplesforsimpletypes.

Type Example Operators Description

Boolean Valididentification={true,false}

=(equals) Trueorfalse.

Enumeration of values

CurrencyofTrade={EUR,USD,CHF,GBP,…}

=(equals)≠(notequals)∈(elementof)∉(notelementof)

Listofvalues.

Number Requestedamount=USDdollaramountwith2decimals

=(equals)<>(less,greater)∈(inrange)

Numberwithunit.

Text (String) ProductID ∋(contains)∌(notcontains)*T(startswith)T*(endswith)

Mostlyusedfordataaccep-tance/validationtesting.

Table5Simpletypes

Asdiscussedabove,inputobjectsinDMNdiagramscaneitherbesimpletypesorcomplexobjects.Inthecaseofsimpletypes,theinputvalueispasseddirectlyintothedecisiontable(e.g.AUM).Inthecaseofacomplexobject,oneormanyfieldsmustbechosenwhicharesimpletypes(e.g.Customer.age,Location.state).

Sometimes,complexobjectsmaptotechnicalobjects(e.g.JavaclassCustomer).Inothercases,complexobjectsareonlyaconvenientgroupingforbusinesslevel-modelingandonlythefieldsareactuallymappedtotechnicaldatastructures.

Whendevelopingbusinessrules,itisbesttouseasmanywelldefinedlists(enumerations)andnumberranges.Listsandnumberrangescanprovideawiderangeofchoiceindetailingbusinessrules.Inadditiontheserulescanbecheckedforuniquenessandcompleteness.

Recommendation: AvoidusingsimpletypeText,asitdoesnotallowforsophisticatedcompletenessandoverlappingrulesanalysis.Applyenumerationsandnumbersasmuchaspossible.

Page 21 of 22Quick Guide to Decision Modeling using DMN 1.0 – Signavio, Inc., April 2015

5.Conclusion

This“quickstart”setoutthecoreelementsoftheDecisionModelandNotationstandard—decisions,inputdata,knowledgesources,andbusinessknowledgemodels.Theseelementscanbecombinedintodecisionrequirementsdiagramstodescribethedecisionmaking.

Decisionrequirementsdiagramscanspecifyhowdecisionsinaprocessshouldbemade.Theycanalsospecifythelogicsrequirementsfordecisionautomationusingadecisiontable.TheDRDbreaksdowndecisionmakingintoitscomponentpiecesforclarity.Theyshowwhatinformationisrequiredforeachpartofthedecision,aswellaswheretherules,guidelines,policies,andknow-howtomakethedecisioncorrectlycanbefound.

Decisionmodelingisarelativelynewapproachformostorganizations.Thiswhitepaperprovidesthe toolsforuserstoreaddecisionmodelsandrepresentdecisionmodelsinastandardwayasdecisionmodelingisdevelopedasadisciplinealongsideprocessmodeling.Knowingthenotationfordecisionmodelsisnecessaryfordecisionmodeling,butjustaswithprocessmodeling,thenotationisnotamethodology,anddevelopingeffectivemodelswilllikelytakepracticeandtraining.

Wealsosetoutthelogicelementsofadecisionmodel,especiallythedecisiontable.Logicelementscanbecombinedintodecisionrequirementsdiagramstodescribepreciselyhowadecisioncan beexecuted.Thatis,diagramscanbeextendedwithdecisionlogictoformacompletedefinitionofexactlyhowthebusinesswishestomakeadecision.

TheSignavioProcessManagersupportstheDMNmodelingdescribedhere.Itcreatesacompre-hensiveenvironmentforcollaboratingonthediscovery,managementandimprovementofyourdecisions.WiththeProcessManager,decisionscanbereusedacrossotherdecisionsandtheycanevenbeconnectedwiththeprocessestheydrive.ProcessManagerempowersthepeopleinyourorganizationthatmustmanageeventhemostcomplexdecision.

Page 22 of 22Quick Guide to Decision Modeling using DMN 1.0 – Signavio, Inc., April 2015

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