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8/2/2019 Chapter 8 Constrained Information Models
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Chapter8ConstrainedInformationModels
AcentralideaoftheHL7V3approachisthatofconstrainingorrefiningageneralmodel,for
thespecificusecasebeingconsidered,bylimitingoptionality.Thisideaofconstraininga
generalmodeltocreateanagreedsubsetandinterpretationofthespecificationis
widespreadinthestandardsworld.Suchconstrainedspecificationsarecalledprofiles.
Manystandardshavealargenumberofoptionalaspectsandifdifferentsuppliersdonot
implementthesamesubsettheywillfailtointeroperate.Theuseofprofilesisawayto
enforceaparticularinterpretationtoensureinteroperability.
Theideaofconstrainedinformationmodelscreatesatreelikehierarchyofpossiblemodels.
AttherootliestheRIM.EverythingelseisaconstraintontheRIM.
TypesofConstrainedInformationModel
ThefollowingtypesofconstrainedmodelarerecognisedwithinHL7V3,startingwiththe
broadest,proceedingtothenarrowest.
DMIMDomainMessageInformationModelRMIMRefinedMessageInformationModel
HMDHierarchicalMessageDescription
MTMessageType
DomainMessageInformationModel
DomainMessageInformationModels(DMIM)havebeendefinedformanysubjectareas.
ADMIMisageneralmodelofadomain,inHL7notation,fromwhicharelatedfamilyof
messagespecificationscanbederived.ADMIMmaybecreatedtopdownfromdomain
experienceorbottomupasasupersetofmessagesinadomain.OncecreatedaDMIMcan
beusedareferencefromwhichfurthermessagesmaybedefined.
ADMIMdoesnothaveahierarchicalstructureandcannotbeserialised,whichmeansthatit
cannotbeimplementedasitisbutneedstobefurtherconstrainedasRMIMs.Notall
projectsuseDMIMs,buttheirpurposeistoprovideacommonpointofreferencetoensure
compatibilitybetweenallRMIMsinthesamedomain.
RefinedMessageInformationModel
ThemostwidelyusedconstrainedinformationmodelistheRMIM(RefinedMessage
InformationModel),whichisadiagramofamessagespecification.RMIMsandDMIMsuse
thesamenotation.OneimportantdifferenceisthatanRMIMcanonlyhaveonepointof
entryandcanbeexpressedinaserialisedformat,whichisessentialifamessageistobe
transmittedasastringofbitsoverawire.
HierarchicalMessageDescription
AnRMIMcanalsobeexpressedinatabularformat,knownasahierarchicalmessage
description(HMD).HMDsandRMIMscancontainthesameinformation,butmostpeople
findthatRMIMsareeasiertouseandunderstand.
MessageType
Amessagetype(MT)isaspecificspecificationofamessagewhichcanbeusedinadata
interchange.AnyoneRMIMorHMDcanbefurtherconstrainedinvariouswaystocreatea
setofcloselyrelatedmessagetypes,whicharethenexchangedasalinearstringofXMLand
validatedusinganXMLschema.
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TypesofConstraint
TheRIM,DMIMsandRMIMscanbeconstrainedinseveraldifferentways.
OmissionandCloning
Thesimplestformofconstraintisbyomission.Classesorattributeswithclassesaresimply
leftout.Allclassesandallattributes(apartfromstructuralattributes)intheRIMareoptional,soyouonlyusetheonesyouneed.
Cloning
ThesameRIMclasscanbeusedmanytimesindifferentwaysinDMIMsandRMIMs.This
processisreferredtoascloningandtheclassesselectedforuseinconstrainedmodelsare
referredtoasclones.
ThemetaphorbeingthatyoutakeacloneofaclassfromtheRIMandthenconstrainthat
cloneintheconstrainedinformationmodel.Cloninglimitsthenumberofclassesthatneed
tobedefinedintheRIM,leadingtoasmallstableRIM.
MultiplicityandOptionality
Thenextformofconstraintistoconstrainmultiplicitiesintermsofrepeatabilityand
optionality.MostassociationsandattributesintheRIMareoptionalandallowanynumber
ofrepeats.
Thesecanbeconstrainedbymakingsuchmultiplicitiesnonrepeatablemandatory(1..1)
youneedtohaveone,butonlyone;ornonrepeatableoptional(0..1)ifyouhaveany,you
canonlyhaveone.
InHL7Version3specifications,thecorrectverbformforindicatingarequirementis
"SHALL."Thecorrectverbformforindicatingarecommendationis"SHOULD."Thecorrect
verbformforanoptionis"MAY."Universallyacceptedstandardizationterminologydoesnot
recognize"must"."SHALL"isusedtoindicateamandatoryaspectoranaspectonwhichthereisnooption.ThenegativesareSHALLNOT,SHOULDNOT,MAYNOT.
DataTypesConstraint
Thethirdtypeofconstraintinvolvesconstrainingdatatypes.TheHL7V3datatypeshave
beendesignedwithahierarchicalstructure.Forexampletherearefourcodedatatypes:CS
(codesimple),CV(codedvalue),CE(codewithequivalents)andCD(conceptdescriptor)in
increasingorderofcomplexity.Amorecomplexdatatype,suchasCDcanbeconstrainedto
asimpledatatypesuchasCV.SimilarlythedatatypeGTS(GeneralTimeSpecification)can
beconstrainedtoIVL(TimeInterval)ortoTS(Timestamp).
CodeBinding
Thefinaltypeofconstraintinvolvescodebindingspecifyingwhatcodevaluesetsshallbe
used.ThecodingstrengthofacodemayalsoberestrictedtoCNE(CodedNoExceptions)or
maybespecifiedasCWE(CodedWithExceptions)
Thismayallsoundquitecomplexbutisalotsimplerthanitsounds.Thesimpleruleisthat
youonlyspecifywhatyouneed,leaveouteverythingelseormakeitasimpleaspossible.
VocabularyandValuesets
TheHL7V3standardstalkaboutvocabularydomainsandvaluesetsanditisimportantto
understandthedifferencebetweenthem.
Avaluesetisthesetofcodesthatmaybeusedtopopulateaspecificattributeinamessage
instance,andisusuallyspecifiedbythemessagedesigner.Avaluesetmaybeasinglecode
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only,forexampletospecifyastructuralattribute,asubsetofanHL7definedcode,orallor
partofanexternallydefinedcodingsystem
Avocabularydomainisthesetofcodesavailabletothemessagedesignerforaspecific
attribute.Forexample,thevocabularydomainfortheAct.moodCodeisthesetofallmood
codevaluesdefinedandmaintainedbyHL7.
Messageusersareconcernedwithvaluesets,messagedesignersneedtothinkabout
vocabularydomainsandselecttheirvaluesetsfromthese.
TheconceptofvocabularydomainsismostapplicabletoHL7sowninternallydefined
vocabularytables,whicharequiteextensive.Thesemustbeusedforstructuralattributes
andarewidelyusedwithinDataTypes.
Eachconceptnormallyhasamnemoniccode,whichisthecodevalueused,aprintname
whichexplainsitsmeaningaconceptID,usedforinternalreference,alevelandtype.
Mnemoniccodesareuniqueforaparticularcodingscheme.Thesetableshavea
hierarchicalstructure,witheachconceptbeingallocatedalevel,soalevel2conceptisthe
childoftheprecedinglevel1conceptandsoon.Thecodetypemaybe
Abstract(A)doesnothaveacode,butdoescontainchildconcepts
Specialised(S)hasacodeandcontainschildconcepts
Leaf(L)hasacode,butnochildconcepts
ArtifactNaming
HL7V3artifactsareidentifiedusingacommonnamingscheme,whichisatfirstsightabit
complex.TheformatisSSDD_AAnnnnnnRRVV,
Thefirstfourcharactersidentifythesubsectionsanddomains.
COCT CommonMessageElements
COMT CommonMessageContentFIAB Accounting&Billing
FICR Claims&Reimbursement
MCAI MessageActInfrastructure
MCCI MessageControlInfrastructure
MFMI MasterFileManagementInfrastructure
POLB Laboratory
PORX Pharmacy
PRPA PatientAdministration
PRPM PersonnelManagement
PRSC Scheduling
QUQI QueryInfrastructureRCMR MedicalRecords
Thefirstfourcharactersarefollowedbyanunderscorecharacter_andthentheartefact
type,identifiedwithatwocharacteracronym.
ARApplicationRole
DMDMIM(DomainMessageInformationModel)
DODomain
EXExample
HDHMD(HierarchicalMessageDescriptor)
INInteraction
MTMessageType
NCNarrativeContent
RMRMIM(RefinedMessageImplementationModel)
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STStoryboard
STStoryboardNarrative
TETriggerEvent
Theartifacttypeisfollowedbyasixdigitidentifierallocatedbythecommitterresponsible.
Thefinalcharactersarea2characterRealmCode,wheretheidentifyingwhichinternational
affiliateofHL7isresponsibleforthis.ThedefaultisUV(Universal)followedbyaversion
numberintherange(0099).
Forexample:PRPA_RM001234UV00mayberecognisedasanRMIMinthePatient
Administration,useduniversally,revision00.Thisartifactnamingconventionisabit
awkward,butitisworthtakingthetroubletomemorizethemainacronyms.
ThenameofeachclonedclassinanRMIMisderivedfromitsstructuralattributes.
Fig81ConstrainedInformationModels
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ASimpleExample
Figure82showsasimpleRMIMforaninvestigationreport.
Fig82SimpleRMIM
TheentrypointorfocalclassisanObservationEvent.ThisisthedefaultnameforanyAct
withclassCode=OBS(observation)andmoodCode=EVN(event).Thishasthreeother
attributes:auniqueidentifierid(suchasaUUID),acode,whichstatesthetypeofreport
andaneffectivetime,whichreferstothedate/timeoftheobservation.
ThisreportcontainsoneormoreInvestigationEvents(classCode=INVSTG,moodCode=
EVN),eachofwhichhasanid(suchasaUUIDoralinenumber),acode(inthiscaseaCPT4
codetoindicatewhatitis)andavalue,whichisasimpletextstring(ST).
ThereporthastwoParticipations:SubjectandAuthor.ThewaytoreadtheParticipationsis
thattheObservationEventhassubjectPatientandhasauthorAgent
ThesubjectisaPatient,withanid,suchasahospitalnumber.ThePatientisscopedbyan
Organization,whichhasanagreedidentifier(id).ThecombinationoftheOrganizationidand
thePatientidshouldbegloballyunique.Thepatienthasanoptionalname,inthePersonclass(Entity).Theplayingassociation
(patientPerson)betweenPersonandPatientisindicatedas[0..1],andisnotinboldfont,
indicatingthatthisisnotmandatory.SimilarlythenameattributeinPersonisnotinbold
fontandisannotatedas[0..1].
TheauthorisanAgent,whichcouldbeaclinician,technicianoramachine.TheAgenthasa
uniqueidentifier.
InthisRMIMallelementsaremandatory(andthereforerequired),whichiswhytheyareall
writteninboldfontandsuffixedwiththe*indicator.
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DiagramNotation
Classes
HL7usesaspecialgraphicalnotationforspecifyingRMIMsandDMIMs.
EachActisrepresentedasaredrectangle;
Roleasayellowrectangle
Entityasagreenrectangle.
ActRelationshipisusuallyshownaspink(salmon)arrowshapedpentagon
Participationasacyan(lightblue)pentagon
RoleLinkasalightyellowpentagon.
Eachofthearrowshapedpentagonshasasourcefortherelationshipandatarget.The
directionofthearrowindicatesthemeaningoftheassociation,butthisisnotalwaysthe
waythatthediagramshouldbenavigated.
Thedirectionofnavigation(thewayyoureadthediagram)isindicatedbythelocationofthemultiplicityshownjustoutsidetheclass.Thismaysoundconfusing,buttheimportantthing
torememberisthatthedirectionofthearrowsisnotalwaysthewaythatthediagram
shouldberead.
ActRelationshipandRoleLinkmayberecursive,thatis,pointbacktoitself.Thisisindicated
byapigsearboxwithanotchedoutcornerwhichfitsaroundonecornertheActorRole.
Attributes
EachattributeusesexactlythesameattributenameasisintheRIM.Theattributesselected
foruseinRMIMsareformedbyconstrainingorlimitingtheattributesasdefinedintheRIM.
ThisallowscheckingandvalidationandisisthekeyreasonwhytheRIMmaynotbe
changed.
TheattributenameinanRMIMdiagrammaybeinboldprint.Thisindicatesthatthis
attributeismandatory,itmustalwaysbepresent,nullvaluesarenotallowed.Thisisa
responsibilityofthesenderApplicationRole.
Theattributenamemayhaveastar*nexttoit.Thisindicatesthatthisattributeis
requiredtobepresentinmessages.Ifdataisnotavailableanullvaluemaybesent.
Themultiplicityorcardinalityoftheattributeisdenotedwithinsquarebrackets[]to
indicatehowmanytimesthisattributemayberepeated.[0..1]indicateszeroorone;
[1..1]indicatesexactlyone.*indicatesnoupperlimit,so[0..*]indicateszeroto
many. TheattributesDataTypeisspecifiedaftertheattributename,separatedbyacolon:.
ThespecifiedDataTypemustbeeitherthesameasoravalidconstraintontheRIMData
Typeforthatattribute.
Ifthedatatypeisacode,thenthecodingstrengthmaybedenotedbyaddingeitherCNE
(codednoexceptions)orCWE(codedwithexceptions)afterthedatatypedesignator.
Thevaluesetorvocabularydomaintobeusedwiththisattributeisspecifiedaftereither
an
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Astringinquotes(e.g.string)indicatesadefaultvalueforthisattribute.
Finally,abriefdescriptionofattributesmaybeincluded,enclosedwithinparentheses
(..).
Iftheattributeinformationextendsbeyondoneline,thensecondandsubsequentlinesare
indented.EntryPoint
EveryRMIMhasanentrypoint,whichpointstothefocalclass.Thisalsostatesitsname,
identifierandanydescriptivenotestheauthorhasprovided.
CMET
CommonMessageElementTypes(CMET)isareusablemodules,whichcanbeusedin
multiplemessages,ratherlikeaprogramsubroutine.UsingCMETscanspeedupthe
processofdevelopingmessagesandincreaseconsistencybetweendifferentspecifications.
EachCMEThastwoparts.TheCMETreferenceisaspecialclass,whichcanbeaddedtoan
RMIM.WhenaCMETisreferenced,orusedinanotherdiagram,itisshownwithaspecialnotation,aboxwithdashededges.ItcontainsthenameoftheCMET,itsartifactid,itsclass
codeanditslevelofattribution.Itiscolourcodedinamannerconsistentwithitsrootclass.
EachCMEThasauniqueartifactidentifier(beginningwithCOCT_),whichistheprimarylink
betweeneachCMETreferenceanditscontent.
TheCMETcontentitselfisdefinedasasmallRMIM,whichisstoredinaCMETlibrary.Thisis
includedautomaticallyinmessageswhentheyareconstructed.
EachCMEThasasingleentrypoint,whichisthepointatwhichitisattachedtoany
containingmessage,whichreferencesit.CMETsdonothaveexitpoints,whichmeansthey
havetobeattheterminalorleafpointinthehierarchicalstructureofamessage.
BecauseCMETsaredesignedforcommonusebyanyHL7committeetheyarekeptinaseparatecommoncomponentslibrary.
ChoiceBox
HL7RMIMsshowchoicesoroptionsbyusingachoicebox.Eachoftheoptionsisshownin
aboxwithadashedlineborder,fromwhichasinglechoiceismade.
Associationsmaybemadetoaspecificclasswithinthechoicebox,ortoanyoftheclasses,
irrespectiveofwhichisselected.
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Fig83HL7V3DiagramNotation
Tooling
RMIMsarebuiltusingaspecialtoolsetdevelopedbyHL7.Theoriginaltools,basedon
MicrosoftAccessandVisioareintheprocessofbeingreplacedbyanewgenerationoftools,
whichuseaslightlymodifiednotation.
ThebasisofthesetoolsisasetofinterrelatedXMLschema,knownasModelInterchange
Format(MIF).MIFdefinestheprimaryartifactsthatcanbedevelopedorexchangedasa
resultofHL7V3standardsdevelopmentandimplementation.
Templates
InHL7,templatesareusedtoconstrainandverifyconformancetoprofiledHL7Version3
RefinedMessageInformationModels(RMIMs).Atemplateisanexpressionofasetof
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constraintsontheRIM,whichisusedtoapplyadditionalconstraintstoaportionofan
instanceofdataexpressedintermsofsomeotherStaticModel.Templatesareusedto
furtherdefineandrefinetheseexistingmodelswithinanarrowerandmorefocusedscope.
EachtemplateisidentifiedwithatemplateID,agloballyuniqueidentifier.
HL7DevelopmentFrameworkHL7sstandarddevelopmentmethodologyisdocumentedintheHL7Development
Framework(HDF)1.TheHDFiswrittenforHL7memberswhoaredevelopingstandards
withinHL7committees.Howevermuchofwhatitsaysisofuniversalrelevance.TheHDF
adoptsaprojectorientedapproach,basedonaProductLifeCycleforProductDevelopment.
TheHDFidentifiesthefollowingmajorstages:
ProjectInitiation
TheProjectInitiationProcess(PIP)includesinitiation,planning,andapprovalsubstages,
includingthedevelopmentofadetailedProjectScopeStatement(PSS)andplan.The
projectplanidentifiesthebusinesscaseandobjectives,participantsincludingsponsor
committee,projectleader,contributorsandearlyimplementersandatimeschedule.
DomainAnalysis
DomainAnalysisProcess(DAP)includesanalysisandrequirementsdocumentation,including
thedevelopmentofaDomainAnalysisModel(DAM),whichincludes:
Businesscontextincludingdocumentationusingstoryboardsandidentificationof
relevantactorsandinteractions
Usecaseanalysisdocumentingusecasesandactors
Processmodel,documentedusingactivitydiagrams
Informationmodel,documentedusingclassesandattributes
Businessrulesincludingtriggerevents
Glossary
SpecificationDesign
SpecificationDesignProcess(SDP)isthecoreoftheprocess.Itinvolvesmappingthe
requirementsassetoutintheDomainAnalysisModeltotheHL7RIM,datatypesand
vocabularytospecifythemessagestructures,valuesetsanddynamicprocesses.
Profiles
Aprofileisasetofinformationusedtodocumentsystemrequirementsorcapabilitiesfromaninformationexchangeperspectiveandisexpressedintermsofconstraints,extensions,or
otheralterationstoareferencedstandardoranotherprofile.ProfilesofHL7Version3are
derivedfromaVersion3specification,asballotedeitherbyHL7orbyoneofitsaffiliates.
Thecategoriesanduseofprofilesincludeannotation,constraint,localizationimplementable
andconformanceprofiles.
AnnotationProfile
Annotationprofilesdocumentthestandardexactlybutwithmoreinformationtofurther
explainthebasedocumenttoeducateprospectiveusersand/orimplementers.
ConstraintProfile
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Constraintprofilesmaycontainunchangedandconstrainedelements,reducingthe
optionalityandcardinalityofthebasespecification(i.e.,theHL7V3standard)inorderto
makethespecificationmoreexact.
LocalizationProfile
Localizationprofilesmeetthesameobjectivesasaconstraintprofile,withtheadditionofsomeadditionalelements(extensions).HL7Version3allowslocalizationofsomepartsof
thestandardbutnotothers.Inparticular,HL7doesnotallowanyone,apartfromHL7itself
throughaformalprocess,tochangeormodifytheRIMoranyoftheDataTypes.
Localizationcanmakefulluseoftheconstraintmechanismsandmakecertainchangesto
RMIMs,DataTypes,MessageTypes,CMETsandVocabularies.
ImplementableProfile
Implementableprofilesarethemostconstrainedconstraintprofilesandeliminateall
optionalityinthebasespecification(theHL7V3standard)inordertomakethespecification
exactandapproach"plugandplay"interoperability.Optionalityforaprofileiseliminated
whentheconformanceindicatorforeveryattributeandassociationiseitherRequiredor
NotPermittedandeveryvocabularydomainisboundtoavalueset.
ConformanceStatement
Conformancestatementssetoutacomputersystem'sconformanceclaimtoasetof
interactions.Aconformanceprofileindicatesthesetofinteractionsthatacomputersystem
(orapplicationrole)supports.Itimpliesacommitmenttofulfilalloftheresponsibilitiesof
theinteractionsspecifiedandtoimplementfaithfullytheartifactsthatconstitutethe
interactionsandanyfurtherconstraintsorextensions.
ImplementationTechnologySpecification(ITS)
TheXMLimplementationtechnologyspecificationdescribeshowindividualinstancesof
messagetypesshallberenderedinXMLforserialtransmissionoverthenetworkandthe
structureofschemasusedtovalidateeachinstance.NotethattheHL7generatedXML
schemasarenotabletotestalloftheconstraintsdefinedinaHL7messagedefinition.
Thegenerationoftheschemasandmessagerepresentationisdoneautomatically.Those
notdirectlyinvolvedinthatprocessdonotneedtounderstandthetechnicaldetails.Thekey
pointsasfollows:
OneXMLelementisdefinedtocorrespondtoeachrowintheHMDgrid,withtheexception
ofstructuralattributeswhichareexpressedasXMLattributes.
EachDataTypehasadefinedXMLrepresentation.TherestrictionbasefeatureinanXML
schemaisusedextensivelytodefinehowdatatypesareimplemented.
TheschemafilesforCMETsaresuppliedseparatelyandthenusedbyeachmessageschema
asrequired.
TheXMLschemasdefinedsupportV3DataTypes,andDataTyperefinement,throughthe
useoftheW3CSchemarestrictionelement.Additionalstandardschemasectionssupport
RIMclassesandtheHL7definedvocabularydefinitions.Theseschemasectionscanbe
selectivelycombinedwithaspecificmessageschemathroughtheincludefunctioninthe
XMLschemastandard.
HL7messagesallsharethesameXMLnamespace.
Messageversioninformationisconveyedasattributeswithinthemessageratherthanby
changestothenamespaceidentifier.
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Fig84HL7DevelopmentFramework
Documentation
HL7V3documentationisvoluminous.ThefullsetofHL7V3standardsispublishedannually
andcanbedownloadedformtheHL7website( www.hl7.org).
FoundationDocuments
Foundationdocumentsarethebasisofthestandard.ThefollowingFoundationdocuments
in2008contain359,000words(about30hoursreadingat200wordsperminute.Inadditionthereare30ormoredomainspecificstandardscovering:
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Fig85HL7Version3Documentation
1
HL7 Development Framework. Version 1.3, 2009