Ontology & Semantic Web
–
A
Dummy’s Overview of Modern
Technologies for Sharing Knowledge
Mitsunori Ogihara
Center for Computational Science
What Is an Ontology?
•
Merriam
-
Webster: “The branch of
metaphysics dealing with the nature of being”
–
What does it mean to exist?
–
What exists?
•
In the field of computer science an ontology is
“a specification of a conceptualization”
–
Tom
Gruber
World, Specification,
Conceptualization
•
Human observes
the world and
conceptualizes it
•
That human
conceptualizatio
n is put into a
specification
•
The world
matches the
specification
What an Ontology Can Conceptualize
•
Things to exist
–
Individuals, not necessarily physical existence
–
Classes of individuals
•
Relations among things
–
Is a part of
–
Is not equal to
•
Properties about things
–
Has a value of
Problem
•
Conceptualization is ambiguous and
inaccurate
–
How a person A sees the world is not necessarily
equal to how a person B sees the world
•
Specification is difficult
–
Formal specification is tiresome
•
How efficiently can one develop an ontology?
•
How efficiently can one compare
ontologies
?
Why Was the Idea of Ontology
Created?
•
Artificial Intelligence … a branch of computer
science that studies computational methods
of mimicking human intelligence
•
Intelligence includes ability to
–
Understand data obtained through senses
–
Acquire knowledge
–
Apply knowledge to solve problems
–
Understand emotion
Knowledge Representation
•
An area that studies how to formally think
–
[Davis,
Shrobe
, and Solovitz’93] Knowledge
Representation is
•
A surrogate
•
A set of ontological commitments
•
A fragmentary theory of intelligent reasoning
•
A medium for efficient computation
•
A medium of human expression
–
Commitments are filters through which the world
is observed
Semantic Web
•
The first generation of Web is HTML
(Hypertext Markup Language)
–
This is designed so as to present texts in a format
specification that can be easily understood and
rendered
–
Search engines can find documents that may
contain certain information by using keyword
matches, but can’t find an answer to a question
Semantic Web
•
A new generation of web should provide not texts but
structured information, a part of which may be texts
–
Resource Description Framework (where the resources
are)
–
XML (Extensive Markup Language)
•
A user
-
definable format
•
Documents conforming to the format
•
Idea:
–
Decide on what information can a web page might contain
–
Decide on how to describe such information
–
Annotate the web page with such information in a
predetermined format
Ontology Development Tools
•
OWL (Web Ontology Language)
–
Currently the most popular ontology description
language
–
http://www.w3.org/TR/owl
-
features/
–
OWL DL (Description Logic, standard version)
–
OWL
Lite
(restricted version) … basic constructs
exist to logically express constructs of DL
–
OWL Full (for RDF)
–
http://www.cs.manchester.ac.uk/~horrocks/ISWC
2003/Tutorial/examples.pdf
A History of Ontology Description
Languages
•
KIF (1992) … Stanford, first
-
order logic
•
Loom (1992) … USC, first
-
order logic, for KR
nor necessarily for ontologies
•
FLogic (1995) … Karlsruhe, combination of
first
-
order logic and frames
•
OKBC (1997) … DARPA
•
XOL (1999) … SRI, an XML version of OKBC
•
OWL (2001) … W3C
Ontology Development Tools
•
Created along with development of
description languages
Popular Free Tools
•
Protégé
-
2000
•
Swoop … an open source project, hosted at
Google
Ontology Building Process
•
Vocabulary
–
Need to settle on a set of words to be used to describe the
domain knowledge (or the domain of the web contents)
–
Where to start? Thousands of words?
•
Knowledge Base Building
–
Express domain experts’ knowledge in terms of ontology
–
Who will translate knowledge into logical forms?
Ambiguity issues?
•
Inference
–
Make new discovery
–
Identify classes and properties of an individual
–
Inference engines, compute
-
intensive
Exporting Ontologies
•
Protégé and Swoop (and others) have the
ability to export/import data in various
formats
–
Enables information exchange between ontologies
Finding a Nice Mapping
•
A mapping
f
of an ontology O to an ontology O’ is one that
maps each class of O to a class of O’ and each property of O
to another property of O’. We want:
–
For all classes
c
and
d
of O,
c
is a subclass of
d
if and only if
f(c
) is
a subclass of
f(d
) in O’
–
For all class
c
and property
p
of O,
c
has property
p
if and only if
f(c
) has property
f(p
) in O’
•
Finding a perfect mapping is hard, and practically such a
perfect mapping rarely exists
•
Finding a mapping that maximizes a certain quantity is also
difficult, and is NP
-
hard
–
Heuristic methods are usually used (based on graph properties)
References
•
T.R.Gruber
(1993), A Translation Approach to Portable Ontology
Specifications, Knowledge Acquisition
•
V.Devedzik
(2002), Understanding ontological engineering,
Communications of the ACM
•
J.Gennari
,
M.Musen
,
R.Fergerson
(2003), The evolution of Protégé:
an environment for knowledge
-
based systems development,
International Journal of Human
-
Computer Studies
•
A.Kalyanpur
,
B.Parsia
,
E.Sirin
,
B.Grau
(2006), Swoop: A web
ontology editing browser, Web Semantics: Science
•
O.Corcho
et al. (2003), Methodologies, tools and languages for
building
ontologies
. Where is their meeting point?
Data&Knowledge
Engineering
•
L.Lacy
(2005), OWL: Representing information using the web
ontology language
•
J.Euzenat
, P.
Shvaiko
(2007), Ontology Matching, Springer
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