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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
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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
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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
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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
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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
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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?
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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.
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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
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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
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Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität PotsdamTurmbau zu Babel, Pieter Brueghel, 1563
9
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)
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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
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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
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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