Ontologies Part 1

8/4/2019 Ontologies Part 1

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Dr. Hoang Huu Hanh, SoST DoIT, HUSC

hanh-at-hueuni.edu.vn


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IntroductiontoOntologies

OntologyEngineering

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Section1


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OntologyinPhilosophy: Themetaphysicalstudyofthenatureofbeing

andexistence

OntologyinArtificialIntelligence:

asharedandcommonunderstandingofsomedomainthatcanbecommunicatedbetweenpeopleandapplicationsystems (Gruber)


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Ontology(languages)fortheSemanticWeb:

Weaimata(XMLbased)languagetoformallydescribeconcepts,instances,relationsandaxioms,i.e.data+structureinordertoenablemachineprocessablereasoningonand

exchangeofdata.

Knowledgerepresentation,exchange,combination(inferenceofnewknowledge!)

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Ontologiesarecontenttheoriesaboutthesortsof

objects,propertiesofobjects,andrelations

betweenobjectsthatarepossibleinaspecifieddomainofknowledge.

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OntologyasvocabularyOntologyisarepresentationvocabulary,oftenspecializedtosomedomainorsubjectmatter.

OntologyascontenttheoryThemaincontributionofontologyistoidentifyspecificclassesofobjectsandrelationsthatexistinsomedomain.

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Studer(98): Formal,explicitspecificationofasharedconceptualization

Machine

readable

Concepts,properties,functions,axiomsareexplicitlydefined

Consensual

knowledge

Abstractmodelofsomephenomenaintheworld

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Concepts:Classes+classhierarchy

instances Properties:oftenalsocalledRolesorSlots

labeledinstancevaluepairs Axioms/Relations:

relations

between

classes

(disjoint,

covers) inheritance(multiple?defaults?)

restrictionsonslots(type,cardinality)

Characteristicsofslots(symm.,trans.,)

reasoning

tasks:

Classification:Whichclassesdoesaninstancebelongto?

Subsumption:Doesaclasssubsumeanotherone?

Consistencychecking:Isthereacontradictioninmyaxioms/instances?

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Ontologicalanalysisclarifiesthestructureof

knowledge.

Ontologiesenableknowledgesharing.

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Welldesigned

Usefulandprovenmodellingprimitives Intuitivetohumanusers Expressiveenough

Efficient

and

complete

reasoning

support Welldefined clearsyntax readontologies Formalsemantics understand(process)ontologies to

facilitatemachineinterpretationofthatsemantics Compatible Easymapping to/fromotherontologylanguages

MaximumcompatibilitywithXMLandRDF(S)

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Section2


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OntologyEngineering: Definingtermsinthe

domainandrelationsamongthem Definingconceptsinthedomain(classes)

Arranging

the

concepts

in

a

hierarchy

(subclass

superclasshierarchy)

Definingwhichattributesandproperties (slots)

classes

can

have

and

constraints

on

their

values Definingindividuals andfillinginslotvalues

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Screenshotsinfurtherexamplesarefrom

Protg,which:

isagraphicalontologydevelopmenttool

supportsarichknowledgemodel isopensourceandfreelyavailable

(http://protege.stanford.edu/)

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Whatisthedomainthattheontologywillcover? Forwhatwearegoingtousetheontology? Forwhattypesofquestionstheinformationin

theontologyshouldprovideanswers

(competencyquestions)?

Answerstothesequestionsmaychangeduringthelifecycle

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French winesandwine regions

Californiawines and

wine regions

Which wineshould

I serve withseafood

today? A sharedONTOLOGY

of

wine and food


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WhichwinecharacteristicsshouldIconsider

whenchoosingawine? IsBordeauxaredorwhitewine?

Does

Cabernet

Sauvignon

go

well

with

seafood? Whatisthebestchoiceofwineforgrilledmeat? Whichcharacteristicsofawineaffectits

appropriatenessforadish? Doesaflavororbodyofaspecificwinechange

withvintageyear?

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wine,grape,winery,location,...winecolor,winebody,wineflavor,sugarcontent,...

whitewine,redwine,Bordeauxwine,...food,seafood,fish,meat,vegetables,cheese,...

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Aclassisaconcept inthedomain aclassofwines

aclassofwineries

a

class

of

red

wines

Aclassisacollection ofelements(instances

ofclasses)withsimilarproperties

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Classesusuallyconstituteataxonomichierarchy (a

subclasssuperclass hierarchy) AclasshierarchyisusuallyanISAhierarchy:

aninstanceofasubclassisaninstanceofasuperclass Ifyouthinkofaclassasaset ofelements,a

subclassisasubset

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AppleisasubclassofFruit

Everyappleisafruit RedwinesisasubclassofWine

Everyredwineisawine ChiantiwineisasubclassofRedwine

EveryChiantiwineisaredwine

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topdown definethemostgeneralconcepts

firstandthenspecializethem bottomup definethemostspecific

conceptsandthenorganizetheminmoregeneralclasses

combination definethemoresalient

concepts

first

and

then

generalize

and

specializethem

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Classes(andslots)usuallyhave

documentation

Describingtheclassinnaturallanguage

Listingdomainassumptionsrelevanttotheclassdefinition

Listingsynonyms

Documentingclassesandslotsisas

importantasdocumentingcomputercode!

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Slotsinaclassdefinitiondescribeattributes

ofinstancesoftheclassandrelationstoother

instances

Eachwinewillhavecolor,sugarcontent,producer,etc

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Typesofproperties intrinsicproperties:flavor andcolor ofwine extrinsicproperties:name andprice ofwine

parts: ingredients inadish

relationstootherobjects:producer ofwine(winery)

Simpleandcomplexproperties simpleproperties(attributes):containprimitivevalues

(strings,numbers)

complexproperties:contain(orpointto)otherobjects

(e.g.,awineryinstance)

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(in

Protg

2000)


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Asubclassinheritsalltheslots fromthesuperclassIfawinehasanameandflavor,aredwinealsohasanameandflavor

Ifaclasshasmultiple superclasses,itinherits

slotsfromallofthemPortisbothadessertwineandaredwine.Itinheritssugarcontent:highfromtheformerandcolor:redfromthelatter

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Propertyconstraints(facets)describeorlimit

thesetofpossiblevaluesforaslot

ThenameofawineisastringThewineproducerisaninstanceofWineryAwineryhasexactlyonelocation

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Slot

cardinality the

number

of

values

a

slot

has Slotvaluetype thetypeofvaluesaslothas

Minimumandmaximum value arangeofvaluesforanumericslot

Default value thevalueaslothasunless

explicitlyspecifiedotherwise


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Minimumcardinality Minimumcardinality1meansthattheslotmusthavea

value(required)

Minimumcardinality0meansthattheslotvalueis

optional

Maximumcardinality

Maximum

cardinality

1means

that

the

slot

can

have

at

mostonevalue(singlevaluedslot)

Maximumcardinalitygreaterthan1meansthattheslot

canhavemorethanonevalue(multiplevaluedslot)

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String:astringofcharacters(ChteauLafite)

Number:anintegerorafloat(15,4.5) Boolean:atrue/falseflag Enumeratedtype:alistofallowedvalues(high,

medium,low) Complextype:aninstanceofanotherclass Specifytheclasstowhichtheinstancesbelong

TheWineclassisthevaluetypefortheslotproducesattheWineryclass

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Domain ofaslot theclass(orclasses)that

havetheslot

Moreprecisely:class(orclasses)instancesof

whichcanhavetheslot Range ofaslot theclass(orclasses)to

whichslotvaluesbelong

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Asubclassinherits alltheslotsfromthesuperclass

Asubclasscanoverride thefacetstonarrowthe

listofallowedvalues

Makethecardinalityrangesmaller

Replaceaclassintherangewithasubclass

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Wine

Frenchwine

Winery

Frenchwinery

is-a is-a

producer

producer


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Createaninstanceofaclass

Theclassbecomesadirecttype oftheinstance

Anysuperclassofthedirecttypeisatype oftheinstance

Assignslotvaluesfortheinstanceframe

Slotvaluesshouldconformtothefacetconstraints

Knowledgeacquisitiontoolsoftencheckthat

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Thethingstoremember:

Thereisnosinglecorrectclasshierarchy

Buttherearesomeguidelines

Thequestiontoask:Iseachinstanceofthesubclassisaninstanceofits

superclass?

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Theisarelationshipistransitive:

BisasubclassofA

CisasubclassofB

CisasubclassofA Adirectsuperclass ofaclassisitsclosest

superclass

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A

class

can

have

more

than

onesuperclass

Asubclassinheritsslotsand

facetrestrictionsfromalltheparents

Differentsystemsresolve

conflictsdifferently


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Classesaredisjoint iftheycannothavecommoninstances Disjointclassescannothaveanycommonsubclasses either

Redwine,Whitewine,Roswinearedisjoint

DessertwineandRedwinearenotdisjoint

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Wine

Redwine Ros

wineWhitewine

Dessertwine

Port


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Danger

of

multiple

inheritance:cyclesinthe

classhierarchy ClassesA,B,andChave

equivalentsetsofinstances

Bymanydefinitions,A,B,andCarethusequivalent

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All

the

siblings in

the

class

hierarchymustbeatthe

samelevelofgenerality Comparetosectionand

subsectionsinabook


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If

a

class

has

only

one

child,

theremaybeamodeling

problem

IftheonlyRedBurgundywehaveisCtesdOr,why

introducethesubhierarchy?

Comparetobulletsinabulletedlist


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If

a

class

has

more

thanadozenchildren,additional

subcategoriesmaybenecessary

However,ifnonatural

classificationexists,

thelonglistmaybemorenatural


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Awineisnotakindofwines

Awineisaninstance ofthe

classWinesClass

Instance

instance-of


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Classesrepresentconcepts inthedomain,nottheir

names Theclassnamecanchange,butitwillstillreferto

thesameconcept

Synonymnames forthesameconceptarenotdifferentclasses

Manysystemsallowlistingsynonymsaspartoftheclassdefinition

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Whendefiningadomainorrangeforaslot,findthe

mostgeneralclass orclasses

Considertheflavor slot Domain:Redwine,Whitewine,Roswine

Domain:

Wine Considertheproduces slotforaWinery:

Range:Redwine,Whitewine,Roswine

Range:Wine

slotclass allowed values

DOMAIN RANGE


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Aclassandasuperclass

replacewiththesuperclass

Allsubclassesofaclass

replacewiththesuperclass

Mostsubclassesofa

class

consider

replacingwiththesuperclass

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Maker

andProducer

areinverse

slots

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Defaultvalue avaluetheslotgetswhenan

instanceiscreated Adefaultvaluecanbechanged

Thedefaultvalueisacommon valuefortheslot,butisnotarequiredvalue

Forexample,thedefaultvalueforwinebody

canbeFULL

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Anontologyshouldnotcontainall the

possibleinformationaboutthedomain Noneedtospecializeorgeneralizemorethanthe

application

requires Noneedtoincludeallpossiblepropertiesofa

class

Onlythemostsalientproperties

Onlythepropertiesthattheapplicationsrequire

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Ontologyofwine,food,andtheirpairingsprobably

willnotinclude Bottlesize

Labelcolor

Myfavoritefoodandwine Anontologyofbiologicalexperimentswillcontain Biologicalorganism

Experimenter IstheclassExperimenterasubclassofBiological

organism?

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thispresentationisbasedontutorialsandpresentations:

D.Lee,F.Harmelen,M.Arumugam,C.Goble,I.Horrocks,N.F.Noy,

D.L.McGuinness,J.Broekstra,M.Klein,S.Decker,D.Fensel

Ontologies Part 1

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