chapter 8 constrained information models

8/2/2019 Chapter 8 Constrained Information Models

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PrinciplesofHealthInteroperabilityHL7andSNOMED2009TimBenson Chapter8page1

http://www.springer.com/9781848828025

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