Open hpi semweb-06-part1

Semantic Web
Technologies
Lecture 6: Applications in the Web of Data
01: Ontological Engineering

Dr. Harald Sack
Hasso Plattner Institute for IT Systems Engineering
University of Potsdam
Spring 2013
This ﬁle is licensed under the Creative Commons Attribution-NonCommercial 3.0 (CC BY-NC 3.0)

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Lecture 6: Applications in the Web of Data
Open HPI - Course: Semantic Web Technologies
Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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

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

What is an Ontology?

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

Computer Science


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Top-Level Ontology
(Upper Ontology,
Foundation Ontology)

Domain Ontology Task Ontology

Application Ontology

Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam (acc. to Guarino,1998)

The Semantic Gap
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•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.


The Semantic Gap - A Simple Example

•Let‘s model a world:
8 World

C
C B
A B A

Initial State Final State

Modelling 1:
Objects Relations
block A on(X,Y)
block B clear(X)
block C holding(X)
table T handEmpty
hand H

The Semantic Gap - A Simple Example

•Let‘s model a world:
8 World

C
C B
A B A

Initial State Final State

Modelling 1: Modelling 2:
Objects Relations Objects Relations
block A on(X,Y) block A on(X,Y)
block B clear(X) block B clear(X)
block C holding(X) block C onTable(X)
table T handEmpty holding(X)
hand H handEmpty

Modelling and Ontologies
•behind the model there is an ontology
C
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Modelling 1: C
B
Objectx Relations B
A
A
block A on(X,Y) Final State
Initial State
block B clear(X)
block C holding(X)
table T handEmpty
hand H
⊤

entity relation

table block hand binary unary

block A on clear handEmpty
table T block B hand A holding
block C

Axiom: on(X,Y) ⋀ on(Y,Z) → above(X,Z)

Modelling and Ontologies
•behind the model there is an ontology
C
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B
Modelling 2: C
A
Objects Relations A B
Final State
block A on(X,Y) Initial State
block B clear(X)
block C onTable(X)
holding(X)
handEmpty

⊤

entity relation

block binary unary

block A on clear handEmpty
block B holding
block C onTable


Ontological Engineering

•Ontologies enable interoperability among metadata
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•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


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02 - Ontology Design
Open HPI - Course: Semantic Web Technologies - Lecture 6: Applications in the Web of Data
Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

Open hpi semweb-06-part1

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