co-funded by the european union semantic cms community the semantic web – part 2 modeling complex...

Co-funded by the European Union

Semantic CMS Community

The Semantic Web – Part 2

Modeling Complex Knowledge Domains

Copyright IKS Consortium1

LecturerOrganization

Date of presentation

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Copyright IKS Consortium

Content Management The Semantic Web

Storing and Accessing Semantic Data

Semantic Lifting

Knowledge Representation and Reasoning

Knowledge Interaction and Presentation

Designing Interactive Ubiquitous IS

Semantifying your CMS

Reference Architecture for Semantic CMS

Requirements Engineering for Semantic CMS

Part I: Foundations

Part III: MethodologiesPart II: Semantic

Content Management

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Semantic Web Layer Cake


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Semantic Web Layer Cake, Image source: http://www.w3.org/2007/03/layerCake.svg

Unique identification of resources

A format for specifying structured data in a machine-readable form

A model for describing resources with properties

and property values.

A language for querying information specified in

RDF.

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RDF

RDF can be used to make statements about single resources identified by URIs

RDF is able to define relations among resources Literals can be assigned as values to properties of

resources


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http://example.org/myCarhttp://example.org/

Jaguar

http://example.org/rel/Brand

XFhttp://example.org/rel/Model

http://example.org/myCar

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RDF Classes


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http://example.org/myCarhttp://example.org/

Jaguar


http://example.org/VWVehicle

Car

How are these terms related to each other?

Do these terms have anything in common?

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RDF Properties

We need to do statements about properties What is the type of the property?

Definition of valid types for subjects and objects Definition of hierarchies of properties


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http://example.org/UniversityPaderborn


Is “UniversityPaderborn” a valid value for property “Brand”?

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We need to define

a vocabulary for

our domain!

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RDF Schema

“RDF's vocabulary description language, RDF Schema, is a semantic extension of RDF. It provides mechanisms for describing groups of related resources and the relationships between these resources.”

W3C Recommendation RDF Vocabulary Description Language 1.0: RDF Schema

The RDFS namespace is:

“rdfs: http://www.w3.org/2000/01/rdf-schema#”

But RDFS also uses elements from the rdf namespace!


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

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RDF Schema

RDFS does not provide a specific vocabulary for describing properties such as “Brand”, but a language to define vocabularies

RDFS uses RDF to define RDF

vocabularies

Due to it's limited expressiveness,

RDFS is a language to define lightweight ontologies


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”A little semantics goes a long way“

- Jim Hendler

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RDFS Classes

“Resources may be divided into groups called classes. The members of a class are known as instances of the class. Classes are themselves resources.”

The members (resources) of a class A are termed instances of the class A

Classes are resource, e.g. “http://example.org/CarManufacturer” and can be described by RDF properties


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RDFS Classes

The predicate rdf:type assigns the object as type of the subject

The assignment to a type is not exclusive

A subject can be typed by several objects!

Example:


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ex:Jaguar rdf:type ex:CarManufacturer

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RDFS Classes

A resource can be defined as a class explicitly The type rdfs:Class defines a resource as a class

Example:

rdfs:Class is the “class of all classes”, i.e.:


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ex:CarManufacturer rdf:type rdfs:Class

rdfs:Class rdf:type rdfs:Class

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Hierarchies of Classes

“The property rdfs:subClassOf is an instance of rdf:Property that is used to state that all the instances of one class are instances of another.”

The subject and object of the predicate “rdfs:subClassOf” must be instances of rdfs:Class

The property rdfs:subClassOf is transitive

Example:


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ex:CarManufacturer rdfs:subClassOf ex:Company

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RDFS Constructs - Predefined Classes


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rdfs:ResourceAll things described by RDF are called resources, and are instances of the class rdfs:Resource.

rdfs:ClassThis is the class of resources that are classes. rdfs:Class is an instance of rdfs:Class.

rdfs:LiteralThe class rdfs:Literal is the class of literal values such as strings and integers. rdfs:Literal is an instance of rdfs:Class. rdfs:Literal is a subclass of rdfs:Resource.

rdfs:Datatyperdfs:Datatype is the class of datatypes. rdfs:Datatype is both an instance of and a subclass of rdfs:Class. Each instance of rdfs:Datatype is a subclass of rdfs:Literal.

rdf:XMLLiteralThe class rdf:XMLLiteral is the class of XML literal values. rdf:XMLLiteral is an instance of rdfs:Datatype and a subclass of rdfs:Literal.

rdf:Propertyrdf:Property is the class of RDF properties. rdf:Property is an instance of rdfs:Class.


Typos?

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RDFS Properties

“The RDF Concepts and Abstract Syntax specification describes the concept of an RDF property as a relation between subject resources and object resources”

A resource can be defined as property explicitly


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ex:Brand rdf:type rdf:Property

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Hierarchies of Properties

“The property rdfs:subPropertyOf is an instance of rdf:Property that is used to state that all resources related by one property are also related by another.”

The subject and object of the predicate “rdfs:subPropertyOf ” must be instances of rdf:Property

The property rdfs:subPropertyOf is transitive

Example:


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ex:friendOf rdfs:subPropertyOf ex:knows

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Property Restrictions

We need to express, that only subjects and objects of specific types should be used for the predicate “Brand”


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http://example.org/UniversityPaderborn


Is “UniversityPaderborn” a valid value for property “Brand”?

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Domain

“rdfs:domain is an instance of rdf:Property that is used to state that any resource that has a given property is an instance of one or more classes.”

States that each subject with the predicate (property) is an instance of the defined class

If more than one domain is defined, the subjects are instances of all classes!

Example:


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ex:Brand rdfs:domain ex:Vehicle

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Range

“rdfs:range is an instance of rdf:Property that is used to state that the values of a property are instances of one or more classes.”

States that each object of the predicate (property) is an instance of the defined class

If more than one range is defined, the objects are instances of all classes!

Example:


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ex:Brand rdfs:range ex:Company

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RDFS Constructs – Predefined Properties (I)


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rdfs:rangerdfs:range is an instance of rdf:Property that is used to state that the values of a property are instances of one or more classes.

rdfs:domainrdfs:domain is an instance of rdf:Property that is used to state that any resource that has a given property is an instance of one or more classes.

rdf:typerdf:type is an instance of rdf:Property that is used to state that a resource is an instance of a class.

rdfs:subClassOfThe property rdfs:subClassOf is an instance of rdf:Property that is used to state that all the instances of one class are instances of another.

rdfs:subPropertyOfThe property rdfs:subPropertyOf is an instance of rdf:Property that is used to state that all resources related by one property are also related by another.

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RDFS Constructs – Predefined Properties (II)


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rdfs:labelrdfs:label is an instance of rdf:Property that may be used to provide a human-readable version of a resource's name.

rdfs:commentrdfs:comment is an instance of rdf:Property that may be used to provide a human-readable description of a resource.

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RDFS - Example


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ex:CarManufacturer

rdf:type

ex:myCar ex:Jaguarex:Brand

ex:Car

rdf:type

rdfs:domain

rdf:rangeex:Company

ex:Vehicle

rdfs:subClassOfrdfs:subClassOf

RDFAssertional knowledge

RDFS Terminological knowledge

class

class property

class

class

ex:Brand

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Back to the Cake ...


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A language for describing a lightweight ontology.


RDF.

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Why is RDFS not enough?

RDFS cannot express negations

Defined property restrictions are global

Missing cardinalities for properties

Relations between (sub-)classes (e.g. disjunction)


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OWL – Web Ontology Language

“The OWL Web Ontology Language is designed for use by applications that need to process the content of information instead of just presenting information to humans.”

OWL has been developed as a vocabulary extension of RDF

Explicitly represents the meaning of terms in vocabularies and the relationships between those terms. (Ontology)


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http://www.w3.org/TR/2004/REC-owl-features-20040210/

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OWL – The Story

2004 - OWL W3C Recommendation 2009 - OWL 2 W3C Recommendation

OWL = Web Ontology Language

Why not WOL? Obvious pronunciation which is easy on the ear Opens up great opportunities for logos Owls are associated with wisdom It has an interesting back story


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http://lists.w3.org/Archives/Public/www-webont-wg/2001Dec/0169.html

http://piqs.de

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Dialects of OWL

OWL Lite Provides classification hierarchy and simple constraint

features OWL DL (description logic) - Includes OWL Lite

Provides the maximum expressiveness without losing computational completeness and decidability of reasoning systems.

OWL Full - Includes OWL DL Is meant for users who want maximum expressiveness

and the syntactic freedom of RDF with no computational guarantees.


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http://www.w3.org/TR/2004/REC-owl-features-20040210/

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How does OWL look like?

Basic structure of an OWL Document


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<rdf:RDF xmlns:owl ="http://www.w3.org/2002/07/owl#" xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:xsd ="http://www.w3.org/2001/XMLSchema#"> xmlns="http://example.org/">

<owl:Ontology rdf:about=“”> <rdfs:comment>An example OWL ontology</rdfs:comment> <owl:priorVersion rdf:resource="http://example.org/20120101/cars"/>

<owl:imports rdf:resource="http://example.org/20110707/manufacturer"/>

<rdfs:label>Car Ontology</rdfs:label> </owl:Ontology>

...

</rdf:RDF>

RDF DocumentNamespace Definitions

Ontology Header

Importing another ontology

Default Namespace

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Simple OWL Classes

Comparable to RDFS classes Every individual in OWL is a member of the class

owl:Thing Each user-defined class is implicitly a subclass of

owl:Thing OWL also defines the empty class owl:Nothing Definition of domain-specific root classes:


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<owl:Class rdf:ID=“Vehicle”/><owl:Class rdf:ID=“CarManufacturer”/>

Define class

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Hierarchies of Classes

The definition of basic taxonomies for classes can be done by rdfs:subClassOf.

rdfs:subClassOf is transitive.


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<owl:Class rdf:ID=“Car"> <rdfs:subClassOf rdf:resource="Vehicle"/> </owl:Class>

“Car” is a subclass of “Vehicle”

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Disjoint Classes

“The disjointness of a set of classes can be expressed using the owl:disjointWith constructor. It guarantees that an individual that is a member of one class cannot simultaneously be an instance of a specified other class.“


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<owl:Class rdf:about=“Car"> <owl:disjointWith rdf:resource=“Cat”/></owl>

The classes “Car” and “Vehicle” are

disjoint.

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Infer about Disjoint Classes


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<owl:Class rdf:ID=“Car"> <rdfs:subClassOf rdf:resource="Vehicle"/> </owl:Class>

<owl:Class rdf:ID=“Cat"> <rdfs:subClassOf rdf:resource=“Animal"/> </owl:Class>

<owl:Class rdf:about=“Vehicle"> <owl:disjointWith rdf:resource=“Animal”/></owl>

The class “Car” is a subclass of “Vehicle”

The class “Cat” is a subclass of “Animal”

The classes “Vehicle” and

“Animal” are disjoint

It can be inferred, that the classes “Car” and “Cat“are disjoint too!

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Individuals

In addition to the definition of classes, we also need to describe the members of classes (individuals)

Abbreviated representation


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<owl:Thing rdf:ID=“Jaguar"/>

<owl:Thing rdf:about=“Jaguar"> <rdf:type rdf:resource=“CarManufacturer"/> </owl:Thing>

Definition of individual “Jaguar”

Ties the individual to the class

< CarManufacturer rdf:ID="Jaguar"/>

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Simple Properties

“This world of classes and individuals would be pretty uninteresting if we could only define taxonomies. Properties let us assert general facts about the members of classes and specific facts about individuals.“

Property are binary relations. In OWL, two different types of properties are distinguished: object properties, relations between instances of two

classes. datatype properties, relations between instances of

classes and RDF literals and XML Schema datatypes


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

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Object properties relate instances of classes by rdfs:domain and rdfs:range.

Object Properties


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<owl:ObjectProperty rdf:ID=“Brand”>

<rdfs:domain rdf:resource=“Vehicle”/> <rdfs:range rdf:resource=“CarManufacturer”/>

</owl:Thing>

Domain and range for object property

“Brand”

<owl:ObjectProperty rdf:about=“Brand”/>

Properties are defined like classes

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Datatype properties relate class instances and data values using rdfs:domain and rdfs:range.

Datatype Properties


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

<owl:ObjectProperty rdf:ID=“ConstructionYear”>

<rdfs:domain rdf:resource=“Car”/> <rdfs:range rdf:resource=“&xsd;gYear”/>

</owl:Thing>

Domain and range for datatype property “ConstructionYear”

<owl:DatatypeProperty rdf:about=“ConstructionYear”/>

Properties are defined like classes

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Recommended XML Schema datatypes

xsd:string xsd:normalizedString xsd:boolean

xsd:decimal xsd:float xsd:double

xsd:integer xsd:nonNegativeInteger xsd:positiveInteger

xsd:nonPositiveInteger xsd:negativeInteger xsd:byte

xsd:long xsd:int xsd:short

xsd:unsignedLong xsd:unsignedInt xsd:unsignedShort

xsd:hexBinary xsd:base64Binary xsd:unsignedByte

xsd:dateTime xsd:time xsd:date

xsd:gYear xsd:gMonthDay xsd:gDay

xsd:anyURI xsd:token xsd:language

xsd:NMTOKEN xsd:Name xsd:NCName

xsd:gYearMonth xsd:gMonth


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Cardinality Constraints for Properties

owl:minCardinality defines the minimal cardinality for the value of a property.

owl:maxCardinality defines the maximal cardinality for the value of a property.


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<owl:Class rdf:ID=“Vehicle">

<rdfs:subClassOf> <owl:Restriction>

<owl:onProperty rdf:resource=“Wheels”/><owl:minCardinality rdf:datatype=“&xsd;nonNegativeInteger”>2

</owl:minCardinality> </owl:Restriction> </rdfs:subClassOf>

</owl:Class>

Anonymous class Restriction for property “Wheels”

Minimal number of “Wheels” is “2”

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Cardinality Constraints for Properties

“owl:cardinality permits the specification of exactly the number of elements in a relation.”


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<owl:Class rdf:ID=“Motorcycle">

<rdfs:subClassOf> <owl:Restriction>

<owl:onProperty rdf:resource=“Wheels”/><owl:cardinality rdf:datatype=“&xsd;nonNegativeInteger”>2

</owl:cardinality> </owl:Restriction> </rdfs:subClassOf>

</owl:Class>

Restriction for property “Wheels”

Exact number of “Wheels” is “2”

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“The owl:allValuesFrom restriction requires that for every instance of the class that has instances of the specified property, the values of the property are all members of the class indicated by the owl:allValuesFrom clause.”

Local restriction for class definition


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<owl:Class rdf:ID=“Car"> <rdfs:subClassOf>

<owl:Restriction> <owl:onProperty rdf:resource=“preOwner” /> <owl:allValuesFrom rdf:resource=“Person” /></owl:Restriction>

<rdfs:subClassOf></owl:Class>

Restriction on property “PreOwner“ for

instances from class “Car”

Each value is member of class “Person”

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<owl:Class rdf:ID=“Car">

<rdfs:subClassOf><owl:Restriction> <owl:onProperty rdf:resource=“preOwner” /> <owl:someValuesFrom rdf:resource=“Person” /></owl:Restriction>

<rdfs:subClassOf>

</owl:Class>

Restriction on property “PreOwner“ for

instances from class “Car”

At least one value is member of class

“Person”

Relation Implication

allValuesFrom For all cars, if they have a previous owner, all previous owners are persons.

someValuesFrom For all cars, they have at least one previous owner that is a person.

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Property Restrictions with Constants

“owl:hasValue allows us to specify classes based on the existence of particular property values. Hence, an individual will be a member of such a class whenever at least one of its property values is equal to the owl:hasValue resource.”


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<owl:Class rdf:ID=“myCars"> <rdfs:subClassOf> <owl:Restriction>

<owl:onProperty rdf:resource=“Owner”/><owl:hasValue rdf:”JohnMiller”>

</owl:Restriction> </rdfs:subClassOf></owl:Class>

Restriction for property “Owner”

The class “myCar” is defined by value

assignment

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Intersection

owl:intersectionOf defines a class as an intersection of other classes.


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<owl:Class rdf:ID=“CarsFromVW">

<owl:intersectionOf rdf:parseType=“Collection”><owl:Class rdf:about=”Cars”><owl:Class rdf:about=“VW”/>

</owl:intersectionOf>

</owl:Class>

If something is a “Car” and a “VW” it is a

”CarFromVW”

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Union

“owl:unionOf describes a class that contains those individuals that occur in at least one of the class extensions of the class descriptions in the list”.


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<owl:Class rdf:ID=“Gearbox">

<owl:unionOf rdf:parseType=“Collection”><owl:Class rdf:about=”ManualTransmission”><owl:Class rdf:about=“AutomaticTransmission”/>

</owl:intersectionOf>

</owl:Class>

Gearbox is everything that is “ManualTransmission”

or “AutomaticTransmission”.

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Complement

“The owl:complementOf construct selects all individuals from the domain of discourse that do not belong to a certain class.”


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<owl:Class rdf:about=”ManualTransmission”>

<owl:Class rdf:about=“AutomaticTransmission”/> </owl:complementOf ref:resource=“ManualTransmission” /></owl:Class>

“AutomaticTransmission” includes as members all individuals that do not

belong to “ManualTransmission”.

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If you want to know more ...

There is stuff about OWL out there, which is not part of this course: Class axioms Global restriction for properties Logical characteristics of properties

If you are interested in learning more about OWL please check: The W3C OWL Reference (http://www.w3.org/TR/owl-ref) The W3C OWL Guide (http://www.w3.org/TR/owl-guide)

....


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OWL 2

OWL 2 adds new functionality to OWL, while the overall structure is very similar

OWL 2 provides syntactic sugar e.g. disjoint union of classes

Some OWL 2 feature provide new expressivity: keys, property chains richer datatypes, data ranges; qualified cardinality restrictions asymmetric, reflexive, disjoint properties enhanced annotation capabilities


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http://www.w3.org/TR/owl2-primer/

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Back to the Cake ...


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A language for describing a lightweight ontology.


RDF.

Highly expressive ontology language for modelling complex

knowledge domains.

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Lessons Learned

Now you should know ...

... what is the main difference between RDF and ontology languages like RDF Schema and OWL.

... how can RDF Schema be used to build simple ontologies.

... what are the shortcomings of RDF Schema and why is it not enough in some application cases.

... the web ontology language OWL. .. in which sense OWL is more expressive than RDF

Schema.


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References and Additional Material

RDF Vocabulary Description Language 1.0: RDF Schema http://www.w3.org/TR/rdf-schema/

OWL Web Ontology Language Guide http://www.w3.org/TR/owl-guide/

OWL Web Ontology Language Reference http://www.w3.org/TR/owl-ref/

OWL 2 Web Ontology Language Primer http://www.w3.org/TR/owl2-primer/


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co-funded by the european union semantic cms community the semantic web – part 2 modeling complex...

Documents

class rdfs

rdf rdf

property rdfs

instances of rdfs

instance of rdfs

datatype rdfs

rdfs classes resources

carmanufacturer rdfs