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Dr. Harald Sack

Hasso Plattner Institute for IT Systems Engineering

University of Potsdam

Spring 2013

Semantic Web Technologies

Lecture 6: Applications in the Web of Data01: Ontological Engineering

Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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Lecture 6: Applications in the Web of DataOpen HPI - Course: Semantic Web Technologies

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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01 Ontological EngineeringOpen HPI - Course: Semantic Web Technologies - Lecture 6: Applications in the Web of Data

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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What is an Ontology?

„A theory of being, which tries to explain the being itself, by developing a system of universal categories and their intrinsic relationships...“

Philosophy

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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What is an Ontology?

"An ontology is an explicit, formal specification of a shared conceptualization.“

Computer Science

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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Domain Ontology Task Ontology

Application Ontology

(acc. to Guarino,1998)

Top-Level Ontology(Upper Ontology,

Foundation Ontology)

What is an Ontology?

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität PotsdamTurmbau zu Babel, Pieter Brueghel, 1563

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The Semantic Gap

•The Semantic Web is based on the interoperability of metadata

•Among heterogeneous metadata there is a Semantic Gap that can be bridged with the help of ontologies

•Problem of the Semantic Gap:

• different ontologies can be applied to represent identical knowledge.

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität PotsdamTurmbau zu Babel, Pieter Brueghel, 1563

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The Semantic Gap - A Simple Example

•Let‘s model a world:

A

C

B

Initial State Final State

A

C

B

World

Modelling 1:Objectsblock Ablock Bblock Ctable Thand H

Relationson(X,Y)clear(X)holding(X)handEmpty

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität PotsdamTurmbau zu Babel, Pieter Brueghel, 1563

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The Semantic Gap - A Simple Example

•Let‘s model a world:

A

C

B

Initial State Final State

A

C

B

World

Modelling 2:Objectsblock Ablock Bblock C

Relationson(X,Y)clear(X)onTable(X)holding(X)handEmpty

Modelling 1:Objectsblock Ablock Bblock Ctable Thand H

Relationson(X,Y)clear(X)holding(X)handEmpty

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität PotsdamTurmbau zu Babel, Pieter Brueghel, 1563

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Modelling and Ontologies

A

C

B

Initial State Final State

A

C

B

•behind the model there is an ontology

Modelling 1:Objectxblock Ablock Bblock Ctable Thand H

Relationson(X,Y)clear(X)holding(X)handEmpty

⊤

entity relation

table block hand binary unary

handEmptyclear

holding

on

table T hand A

block A

block B

block C

Axiom: on(X,Y) ⋀ on(Y,Z) → above(X,Z)

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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⊤

entity relation

block binary unary

handEmptyclear

holding

onblock A

block B

block C onTable

Modelling and Ontologies

•behind the model there is an ontology

A

C

B

Initial State Final State

A

C

BModelling 2:Objectsblock Ablock Bblock C

Relationson(X,Y)clear(X)onTable(X)holding(X)handEmpty

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

11•Ontologies enable interoperability among metadata

•Therefore, we need

•Methods for efficient development of ontologies(Ontology Design)

•Methods for efficient comparison of ontologies (Ontology Mapping)

•Methods for efficient combination of ontologies (Ontology Merging)

•There are automated methods to support Ontological Engineering:

•Learning new ontologies from a given set of information resources (Ontology Learning)

•Populating existing ontologies with individuals from information resources

Ontological Engineering

Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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02 - Ontology DesignOpen HPI - Course: Semantic Web Technologies - Lecture 6: Applications in the Web of Data