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
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