Wissenstechnologie Iv 08 09

Wissenstechnologie WS 08/09

Michael Granitzer

IWM TU Graz & Know-CenterIWM TU Graz & Know Center

Lect e 4 OWL Infe ence and

http://kmi tugraz at http://www know center at

Lecture 4: OWL, Inference andUpper Ontologies

http://kmi.tugraz.at http://www.know-center.atThis work is licensed under the Creative Commons Attribution 2.0 Austria License. To view a copy of this license, visit http://creativecommons.org/licenses/by/2.0/at/.

TodayToday

RDF Schema (RDFS)

Web Ontology Language (OWL)

OWL & LogicsOWL & Logics

2Example Ontologies

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http://kmi.tugraz.at

Wissenstechnologie @ kmi.tugraz.at

Semantic Web Stack

a.k.a. SW Layer Cakey

a.k.a. SW Tower

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Semantic Web Stack

RDF

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RDF Statements (Triples)A small example

htt // iki di / iki/J h L http://dbpedia org/property/associatedActshttp://en.wikipedia.org/wiki/John_Lennon

http://en.wikipedia.org/wiki/The_Beatles

http://dbpedia.org/property/associatedActs

http://en.wikipedia.org/wiki/Paul_McCartney

rdfs:label


Subject Predicate Object

„Paul McCartney“

j j

http://en.wikipedia.org/wiki/John_Lennon



5http://en.wikipedia.org/wiki/Paul_McCartney



http://en.wikipedia.org/wiki/P Rdfs:label “Paul McCartney”

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aul_McCartney

OntologiesWhat are Concepts in our purpose?What are Concepts in our purpose?

Semiotic Triangle [Ogden & Richards 1923]Semiotic Triangle [Ogden & Richards 1923]

Concept

Refers toSymbolizes

Term / Word/URI

St d fThing

6‚Apache‘

Stands for

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Ontologies & SemanticsExample: MammalExample: Mammal

IntensionIntension

•isA(Vertebrate Animal)•has(Sweat glands)

•withFunction(Milk)•withFunction(hair)

•....

Extension

•Elephant•Lion•Monkey

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Monkey•....

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Summary of Definitions

A Ontology is a model (of the world)

A t l d ib ti l (k l d ) d iA ontology describes a particular (knowledge) domain

A ontologie defines words/terms/signs for describingConceptsConcepts

A ontologie puts concepts into relation to each other

A ontologie uses axioms to put constraints on particularconcepts

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Components of an OntologyComponents of an Ontology

Classes general things of a domainClasses general things of a domain

Instances special things of a domain

R l ti b t thiRelations between things

Properties of things

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Semantics & Communication

Language must allow to express the semantics in an Language must allow to express the semantics in an implementation/algorithmic independent way

Usually done via a Vocabulary

Topic oriented vocabulary (e.g. Friend of a friend)

Schema Knowledge/Terminological Knowledgeg g g

– Special vocabulary to make statements over topic orientedvocabulary (i.e. the termonologie used in a domain)

– A general set of rules independent of the domain– Defines the expressiveness of a language

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Semantic Web Stack

RDF Schema

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RDF Schema (RDFS)http://www w3 org/2000/01/rdf-schema#http://www.w3.org/2000/01/rdf-schema#

Allows to express terminological knowledge over RDFAllows to express terminological knowledge over RDF

Application of RDFS

Defines a new vocabulary for giving meaningDefines a new vocabulary for giving meaningindependent of program logic

Allows to define „lightweight“ Ontologies and basicg g gReasoning capabilities

http://www.w3.org/TR/rdf-schema/

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RDF SchemaClassesClasses

rdfs:Resource Class of all resources

rdfs:Literal Class of literals (Strings)rdfs:Literal Class of literals (Strings)

rdfs:Class Class of classes

rdf:Property Class of propertiesrdf:Property Class of properties

rdf:Statement Class of RDF Statements

…

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RDF SchemaPropertiesProperties

rdf:type Subject is an instance of a class

rdfs:subClassOf Subject is a subclass of a class

rdfs:subPropertyOf Subject is a sub property of a property

rdfs:domain A possible class for a subject of a property

rdfs:range A possible class for an object of a property

rdfs:label human readable label of an resource

rdfs:comment human readable comment of an resourcerdfs:comment human readable comment of an resource

…

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RDFS Semantics

Model based semantics: Model based semantics:

each triple is a sentence

A sentence is tr true, if the triple exists

Entailment: Given a graph the graph is transformed according to therules of RDFS

Implicit knowledge (i e not explicitly modelled)Implicit knowledge (i.e. not explicitly modelled)

#Means of #Means of

#MyBMW

Transportation

rdfs:subClassOf

Transportation

rdfs:subClassOfrdf:type

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#Car

rdfs:subClassOf

rdf:type#Car

rdfs:subClassOf

#MyBMW

rdf:type

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#BMW #BMW

RDFS SemanticsDrawback/Restriction of RDF Drawback/Restriction of RDF

Open world assumption: false statements must be Open world assumption: false statements must be specified

Closed world assumption: if a statement is missing, it is p g,assumed to be false

No negation in RDFS possible

• ex:michael rdf:type ex:nonsmoker

• ex:michael rdf:type ex:smoker• ex:michael rdf:type ex:smoker

Does not lead to a contradiction!

N l i di id l H All

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No rules over individuals e.g. ex:Humans = All ex:Women and All ex:Men

No Counting: “An Elephant has 4 legs”

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No Counting: An Elephant has 4 legs

Semantic Web StackWeb Ontology Language (OWL)Web Ontology Language (OWL)

OWL

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Historical DevelopmentHistorical Development

Standardised since 2004

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DARPA Agent Markup Language (DAML)

Funded by DARPA start 2001Funded by DARPA, start 2001

DARPA: Defense Advanced Research Projects Agencyj g y

Markup Language for semantic nets

DAML ONT: RDFS extension for OntologiesDAML-ONT: RDFS extension for Ontologies

Focus is on the Web

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Ontology Inference Layer (OIL)

European Project with focus on inferenceEuropean Project with focus on inferencecapabilities

Different kinds of standard

Excluding Reification Core OIL is compatible toRDFS

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History DAML+OIL

1999

DARPA Agent Markup Language (DAML) in USA

Ontology Inference Layer (OIL) in EU

2000

Combining both DAML+OIL

2001

DAML+OIL handed in to W3C for standardisastion

Base for Web Ontology Language (OWL)

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Development of OWL

W3C founded 2001 The Ontology (WebONT) Working W3C founded 2001 The Ontology (WebONT) Working Group

Using DAML+OIL for language specificationg g g p

Feb. 2004 the W3C has published the OWL Web OntologyLanguage Recommendations

Simply speaking: They added an additional vocabulary toRDF(S)htt // 3 /2001/ /W bO thttp://w3.org/2001/sw/WebOnt

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OWL - WOL

The language started out as the "Web Ontology Language" The language started out as the Web Ontology Language but the Working Group disliked the acronym "WOL." Wedecided to call it OWL. The Working Group became morecomfortable with this decision when one of the memberscomfortable with this decision when one of the memberspointed out the following justification for this decision fromthe noted ontologist A.A. Milne who, in his influential book"Wi i th P h" t t d f th i h t OWL"Winnie the Pooh" stated of the wise character OWL:

"He could spell his own name WOL, and he could spellTuesday so that you knew it wasn't Wednesday "Tuesday so that you knew it wasn t Wednesday...

http://www.w3.org/2003/08/owlfaq

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OWL - WOL

Owl

Winnie the Pooh

24Piglet

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OWL The second storyyhttp://lists.w3.org/Archives/Public/www-webont-wg/2001Dec/0169.html

Jim Hendler wrote:

> ... Dieter is right about that as well) I prefer the three letter WOL to the longer SWOL. How about OWL as a variation. The words would be the same (Ontology Web Language) but it has several advantages: (1) it has just one obvious

i ti hi h i th (2) it t pronunciation which is easy on the ear; (2) it opens up great opportunities for logos; (3) owls are associated with wisdom; (4) it has an interesting back story. OWL has probably been used for many computer languages and projects (see below), but I don't think that is a show stopper.

• But the Background is: "One World Language“ short OWL in the mid 70‘s developed at MIT

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OWL - Specifications

OWL besteht aus 3 UntersprachenOWL besteht aus 3 Untersprachen

OWL Lite

OWL DLOWL DL

OWL Full

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OWL - Specification

The following set of relations hold. The following set of relations hold. Their inverses do not:

Every legal OWL Lite ontology i l l OWL DL t l is a legal OWL DL ontology.

Every legal OWL DL ontology is a legal OWL Full ontology is a legal OWL Full ontology.

Every valid OWL Lite conclusion is a valid OWL DL conclusion.

Every valid OWL DL conclusion is a valid OWL Full conclusion.

27http://www.w3.org/TR/owl-guide/

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OWL Syntax and SemanticNamespace & HeaderNamespace & Header

In addition to rdfs and rdf:In addition to rdfs and rdf:

<rdf:RDF … xmlns:owl = „http://www.w3.org/2002/07/owl#“>

<owl:Ontology rdf:about=„“>

<rdfs:comment>my best ontology</rdfs:comment>

<owl:versinoInfo>v0.5</owl:verisonInfo>

….

</owl:Ontology>

Combines Elements of OWL and RFDS Namespace

28Import of other ontologies possible<owl:imports rdf:resource=uri>

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OWL Syntax and SemanticClasses Individuals and RolesClasses, Individuals and Roles

Classes similar to RDFS (i e subclass of rdfs:Class)Classes similar to RDFS (i.e. subclass of rdfs:Class)

owl:Class

Individuals are similar to instances in RDFSIndividuals are similar to instances in RDFS

Definition via the property rdf:type

<rdf:Description rdf:about=„KlausTochtermann“>f p f „<rdf:type rdf:resource=„Professor“/>

</rdf:Description>

Abbrevated Notation in XML: <Class rdf:about=URI>

<Professor rdf:about=„KlausTochtermann“/>

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OWL Syntax and SemanticRoles (properties in RDF)Roles (properties in RDF)

owl:DataTypeProperty (rdf:Domain ~ rdf:Literal|rdf:DataType|xsd:xxx)owl:DataTypeProperty (rdf:Domain rdf:Literal|rdf:DataType|xsd:xxx)<owl:DatatypeProperty rdf:about=„Name“>

<rdfs:domain rdf:resource=„Professor“/>

<rdfs:range rdf:resource= xsd:String“/><rdfs:range rdf:resource=„xsd:String“/>

</owl:DatatypeProperty>

l Obj tP t ( df D i l Thi )owl:ObjectProperty (rdf:Domain ~ owl:Thing)<owl:ObjectProperty rdf:about=„lecturing“>

<rdfs:domain rdf:resource=„Professor“/>

<rdfs:range rdf:resource=„Lecture“/>

</owl:ObjectProperty>

30owl:annotationPropertyJust for commenting on resources

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OWL Syntax and SemanticSimple Properties between ClassesSimple Properties between Classes

rdfs:subClassOf Similar to RDFSrdfs:subClassOf Similar to RDFS

All classes are sublcasses from owl:Thing

All classes have the sub class owl:NothingAll classes have the sub class owl:Nothing

owl:disjointWith No individual is contained in both classes

/<owlClass rdf:about=„Human“/><owlClass rdf:about=„Animal“>

<owl:disjointWith rdf:resource=„Human“/>

</owlClass></owlClass>

owl:equivalentClass

Two classes are semantically equal

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Two classes are semantically equal

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OWL Syntax and SemanticProperties between IndividualsProperties between Individuals

Owl:sameAs two individuals are the sameOwl:sameAs two individuals are the same

<Professor rdf:about=„KlausTochtermann“/><owl:sameAs rdf:resource=„ProfessorTochtermann“>

</Professor></Professor>

owl:differentFrom two individuals are different

owl:AllDifferent Abrevation for a set of individuals owl:AllDifferent Abrevation for a set of individuals owl:distinctMembers

<owl:AllDifferent><owl:AllDifferent><owl:distinctMembers rdf:parseType=„Collection“>

<Person rdf:about=„MichaelGranitzer“><Person rdf:about=„MarkusStrohmaier“><Person rdf:about KlausTochtermann“>

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<Person rdf:about=„KlausTochtermann“></olw:distinctMembers>

</owl:AllDifferent>

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OWL Syntax and SemanticProperties between IndividualsProperties between Individuals

owl:oneOf closed classes i e class with a fixedowl:oneOf closed classes, i.e. class with a fixednumber of members

<owl:Class rdf:about=„IWMLecturers“><owl:oneOf rdf:parseType=„Collection“>

<Person rdf:about=„MichaelGranitzer“><Person rdf:about=„MarkusStrohmaier“><Person rdf:about=„KlausTochtermann“><Person rdf:about „KlausTochtermann >

</olw:oneOf></owl:Class>

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OWL Syntax and SemanticLogical Constructors for ClassesLogical Constructors for Classes

Logical construtors on simple“ classes allow to construct newLogical construtors on „simple classes allow to construct newcomplex classes

MenWomenHuman U=

owl:unionOflogical OR

<owl:Class rdf:about=„Women“/><owl:Class rdf:about=„Men“><owl:complementOf rdf:resource=„Women“>

owl:complementOflogical Not

</owl:Class>

<owl:Class rdf:about=„Human“/>

owl:intersectionOflogical AND

<owl:unionOf rdf:parseType=„Collection“> <owl:Class rdf:about=„Men“><owl:Class rdf:about=„Women“>

</owl:unionOf>

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</owl:Class>

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OWL Syntax and SemanticLogical Constructors for ClassesLogical Constructors for Classes

Complex class construtors via role restrictionsComplex class construtors via role restrictions

Defines a class as set of object for which the role has a value ofa specific class

owl:someValuesFrom

owl:allValuesFrom

Owl:hasValue

Cardinality of roles

owl:maxCardinaltiy

owl:minCardinality

35owl:cardinality

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OWL Syntax and SemanticRelationships between Roles/Role PropertiesRelationships between Roles/Role Properties

Relationships between rolesRelationships between roles

owl:subPropertyOf Hierarchy for properties

owl:inverseOf inverse role

Properties of roles

Symmetry role(A,B) = role(B,A)

<MichaelGranitzer, worksTogetherWith,MarkusStrohmaier>

Transitivity role(A,B) && role(B,C) role (A,C)

<Transistor, isPartOf, Chip> && <Chip, isPartOf,Laptop> <Transistor, isPartOf, Chip> && <Chip, isPartOf,Laptop>

<Transisotr,isPartOf,Laptop>

Functional role(A,B) && role (A,C) <B,sameAs,A>

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<MichaelGranitzer, isLecturerOf, Wissenstechnologie>

<GranitzerMichael, isLecturerOf, Wissenstechnologie>

Inverse Functional role(B,A) && role (C,A) <B,sameAs,A>

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OWL Syntax and Semantichttp://www.w3.org/TR/2004/REC-owl-semantics-20040210/

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OWL Full

Highest possible expressiveness using OWL Highest possible expressiveness using OWL

Constraint: Must be valid RDF

D id bilit i t t dDecidability is not guaranteed

No distinction between roles, classes and instances

An instance may be a class of another instance (Meta-modelling)

– <Car rdf:about=„BMW“><BMW rdf:about=„MyBMW“>

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OWL DL

DL….Description Logicsp g

Guranteed to be deciable

Contains all elements of OWL but only some elements of RDFS (mainly rdfs:class and rdf:Property)(mainly rdfs:class and rdf:Property)

Separation of classes, roles and instances

Restrictions on specific roles for classes and instances

Completeness (all implications can be calcualted)

Decidability (all calcualtions can be done in finite time)

With maximum expressiveness

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OWL Lite

Simplest form of OWLSimplest form of OWL

Restriction on class constructors

R t i ti di litRestrictions on cardinality

Predefined class names and role restrictions in specificsituationssituations

Hardly used in practice

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Editors for OWL

Protégé: Protégé: http://protege.stanford.edu/

Altova SemanticWorks (comercial): ( )http://www.altova.com/products_semanticworks.html

SWOOP: htt // i d /2004/SWOOP/http://www.mindswap.org/2004/SWOOP/

TopBraid Composer™ (comercial):http://www topbraidcomposer com/http://www.topbraidcomposer.com/

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OWL Inference and Reasoning

OWL DL uses Description Logics (Beschreibungslogik)OWL DL uses Description Logics (Beschreibungslogik)

DL is a subset of First Order

B fit f L iBenefits from Logic

Well known Logic, studied over years

Known runtime complexibility

Existing algorithms for reasoning

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OWL Inference and ReasoningImportant PropertiesImportant Properties

Expressive Power (Aussdrucksstärke)Expressive Power (Aussdrucksstärke)

What statements can be made over the model?

C t bilit (B h b k it)Computability (Berechenbarkeit)

Can the evaluation algorithm be calculated in finite time?time?

Decideability (Entscheidbarkeit)

Given a logical systems, is there an computablealgorithm to evaluate a given formula? (e.g. decidewhether it is true or false)

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)

Tradeoff: Expressive Power vs. Decideability

Open vs Closed World Assumption

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Open vs. Closed World Assumption

Logic Families

Propositonal LogicPropositonal Logic

Predicate Logic: Formulas contain variables and quantifiers

llcowFeelsWehotwarm →∨ )(Predicate Logic: Formulas contain variables and quantifiers

First Order Logic

D i ti L i– Description Logic

Second Order Logic

Many-sorted logic

…

44Temporal Logic

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Propositonal Logic

ElElements

Atoms: P, Q, R, …

C t t T F l

↔→¬∨∧ ,,,,Constants: True, False

Junctors:

Klammern: ( )Klammern: (, )

ExampleExample

llcowFeelsWehotwarm →∨ )(

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First Order Logic

ElementeElemente

Constants: a, b, John, Animal, Mammal …

Variables: x, y, z, …, y, ,

Functions: f, g,Mapping from constants to constants

P di t P( ) Q( )

Extension to propositional Logic like

Predicate: P(x), Q(y),Mapping von variables to constants

Quantoren: ∃∀ ,

llcowFeelsWehotwarm →∨ )(

Brackets: (, )

Example

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Example

))(()()( xmotherisCowxisCowx →∀

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Description Logics

Knowledge representation via Knowledge representation via

Classes

I di id lIndividuals

Roles (Properties)

Subset of First Order Logic

Family having different languages depending on theexpressiveness

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Description Logic

TBox (terminological box)TBox (terminological box)

Statements over concepts

Class models and class rolesClass models and class roles

ABox (assertional box)

Statements over IndividualsStatements over Individuals

Assignment of Individuals to classes and filling the roles

OWL DL: TBox and ABox are disjunctOWL-DL: TBox and ABox are disjunct

E.g. no Class can be an individual

E g no roles can be individuals

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E.g. no roles can be individuals

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Description LogicsFamily Member ALCFamily Member ALC

ALC – Attributive Language with ComplementALC Attributive Language with Complement

Class, Role and Individual

A i t f I di id l t lAssignment of Individuals to classes

Equivalence, disjunction and conjunction of classes

owl:Thing, owl:Nothing

owl:intersectionOF, owl:complementOf

owl:allValuesFrom, owl:somealuesFrom

rdfs:range rdfs:domain

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rdfs:range, rdfs:domain

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Description LogicsFamily Member SHOIN(D)Family Member SHOIN(D)

SHOIN– Standard OWL-DL LogicSHOIN Standard OWL DL Logic

S: ALC including transitivity of roles

H b t df bP t OfH: sub property, rdfs:subPropertyOf

O: owl:oneOf (closed classes)

I: owl:inverseOf (inverse roles)

N: Restrictions on numbers

D: Allows datatypes (owl:DataType)

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Description LogicsFamily Member SHIF(D)Family Member SHIF(D)

SHIF – OWL LiteSHIF OWL Lite

S: ALC including transitivity of roles

H b t df bP t OfH: sub property, rdfs:subPropertyOf

I: owl:inverseOf (inverse roles)

F: Functional Roles

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OWL –DL Reasoning

Application AreasApplication Areas

Taxonomy classification: Computes an inferred class hierarchy from the asserted definitions

Consistency checking: Detects classes that cannot have any instances

Instance classification: Finds all classes that a given individual belongs to

State-of-the-Art are so called tableaux algorithms for reasoningState of the Art are so called tableaux algorithms for reasoning

Worst case time compelxity is exponential, for practicalproblems usually faster

52http://www.cs.man.ac.uk/~ezolin/dl/

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DL Resources

OWL Reasoning Examples OWL Reasoning Examples http://owl.man.ac.uk/2003/why/latest/

Description Logicp gThe Description Logic Handbook: Theory, Implementation, and Applications. F. Baader et al., Cambridge University Press 2003 ISBN 0521781760 Cambridge University Press, 2003. ISBN 0521781760

http://dl.kr.org/

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DL (OWL) Reasoner

Racer (commercial): Racer (commercial): http://www.racer-systems.com/

FaCT++: http://owl.man.ac.uk/factplusplus/

Pellet: htt // ll t ldl /http://pellet.owldl.com/

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A Short Protege DemoDo you know mad Cows?Do you know mad Cows?

55http://protege.cim3.net/cgi-bin/wiki.pl?ProtegeOWLDLReasoning

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Ontology Types and ExistingRessourcesRessources

Upper Level OntologiesUpper Level Ontologies

Aka Top-Level Ontology, Foundation Ontology

M d l f bj tModel of common objects

Common Sense Knowledge/ General models of theWorldWorld

Domain Ontologies

Model for a specific domain (i.e. Genes, Biomedical Engineering etc.)

F d l th li ti

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Focused also on the application use case

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Upper Level Ontologies

Formal Upper Level OntologiesFormal Upper Level Ontologies

Suggested Upper Merged Ontology (SUMO)

DOLCEDOLCE

(Open)Cyc

Basic Formal Ontology (BFO)

…

Informal Upper Level Ontologies

DublinCore

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DublinCore

WordNet

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SUMOSuggested Upper Merged Ontology (SUMO)

From IEEE Working Group 1600 p1

Suggested Upper Merged Ontology (SUMO)

From IEEE Working Group 1600.p1

Largest free, formal ontology available, with 20,000 terms and 70,000 axioms when all domain ontologies are , gcombined. (http://www.ontologyportal.org/)

Mapping to Word Net

Demo

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WordNethttp://wordnet princeton edu/http://wordnet.princeton.edu/

Lexical Ontology for (English) LanguageLexical Ontology for (English) Language

Classes: Nouns, Verbs, Adjective, Adverbs

G d i t S tGrouped into Synsets

Relations between Synsets: hypernym, hyponym, holonym meronym troponymholonym, meronym, troponym…

220,000 Words; 128,000 Synsets

Limitations

No pronouncation and irregulary verbs

59No domain specific vocabulary

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Cyc

Largest project to capture human knowledgeLargest project to capture human knowledge

Formalized representation of a vast quantity of fundamental human knowledgeg

Started 1986, Cycorp spin off 1994

Properitery System using predicate logic and LISP similarProperitery System using predicate logic and LISP similarsyntax

Structured in micro theories and assertionsStructured in micro theories and assertions

Open Source Version available as OpenCyc

htt //

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http://www.opencyc.org

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Cychttp://www.cyc.com/cyc/technology/whatiscyc_dir/whatdoescycknow

What Cyc knows“What Cyc „knows ….

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Summary

OWL Syntax adds means to express complex classes andOWL Syntax adds means to express complex classes andlogics over RFDS

OWL-DL,OWL-Lite, OWL-Full, ,

Formal Logical Theories for Reasoning

Description Logic for OWLDescription Logic for OWL

Abox, Tbox

Upper Ontologies vs. Domain Ontologies

SUMO, WordNet, OpenCyc

62Linking Open Data

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Points you should take away from thislecturelecture

• What OWL adds to RDFS?What OWL adds to RDFS?

• Types of OWL and Reasoning capabilities?

• Use existing Ontologies/Upper Level Ontologies• Use existing Ontologies/Upper Level Ontologies

• What is Linking Open Data?

Next Week:Next Week:

• Ontology ModellingRules of Thumb for modeling ontologiesRules of Thumb for modeling ontologies

• Ontology Alignment & Matching

63• Semantic Web Frameworks:

Jena/Sesame with Examples

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That‘s it for today…

Thanks for your attention

Questions/comments?

i @[email protected]

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License

This work is licensed under the Creative Commons This work is licensed under the Creative Commons Attribution 2.0 Austria License. To view a copy of this license, visit http://creativecommons org/licenses/by/2 0/at/http://creativecommons.org/licenses/by/2.0/at/.

Contributors:

Mathias Lux

Peter Scheir

Klaus Tochtermann

65Michael Granitzer

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Education

Wissenstechnologie Iv 08 09