Keynote at Diffuse conference, Brussels, 2002

1. The Semantic Web:
Status and Prospects
Guus Schreiber
University of Amsterdam
Co-chair W3C Web Ontology Working Group

2. 2
The Evolving Web
Web of
Knowledge
HyperText Markup Language
HyperText Transfer Protocol
Resource Description Framework
eXtensible Markup Language Self-Describing Documents
Foundation of the Current Web
Proof, Logic and
Ontology Languages
Shared terms/terminology
Machine-Machine communication
1990
2000
2010
Berners-Lee, Hendler; Nature, 2001
DOCUMENTS
DATA/PROGRAMS

3. 3
Semantics for the Web:
some challenges
 Machine-processable representation of
semantic information
 Defining semantics in an OPEN environment
• Adding semantics to other people’s semantics
• Ability for everyone to contribute
 Ability to define mappings between semantic
representations
• Semantic representations are context-dependent,
but commonalities can/must be captured
 Creating a critical mass of semantic content
• In the end, this will be the critical success factor

4. 4
W3C’s view on Web Semantics
Semantic Web LayerCake (Berners-Lee, 99;Swartz-Hendler, 2001)

5. Semantic web languages provide
“external” referents for XML documents
CV
name
education
work
private
< >
< >
< >
< >
< >
< Χς >
< ναµε>
<εδυχατιον>
<ωορκ>
<πριϖατε>
CV
name
education
work
private
< >
< >
< >
< >
< >
< Χς >
< ναµε>
<εδυχατιον>
<ωορκ>
<πριϖατε>
CV
name
education
work
private
< >
< >
< >
< >
< >
< Χς >
< ναµε>
<εδυχατιον>
<ωορκ>
<πριϖατε>
SW languages add mappings
And structure.

ωορκ
ϖατε
εδυχ Χς
ΧςΧς
Χς

CV
name
education
work
private
< >
< >
< >
< >
< >
<  >
< >
< >

<⇐⇑©∨>
CV
name
education
work
private
< >
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<  >
< >
< >
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<⇐⇑©∨>
CV
name
education
work
private
< >
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<  >
< >
< >

<⇐⇑©∨>
CV
name
education
work
private
< >
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<  >
<  >
<  >

< ⁄‹›„ >
CV
name
education
work
private
< >
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<  >
< >
< >

<⇐ ⇑ © ∨>

6. 6
What is an Ontology?
 In philosophy: theory of what exists in the
world
 In IT: consensual & formal descriptionconsensual & formal description
of shared concepts in a domainof shared concepts in a domain
– Aid to human communication and shared
understanding, by specifying meaning
– Machine-processable (e.g., agents use
ontologies in communication)
 Ontology = key technology inOntology = key technology in
semantic information processingsemantic information processing
– Applications: knowledge management, e-business,
industrial engineering, semantic world-wide web

7. 7
Typical semantic-web use case:
image search
 A person searches for
photos of an “orange ape”
 An image collection of
animal photographs
contains snapshots of
orang-utans.
 The search engine finds
the photos, despite the
fact that the words
“orange” and “ape” do not
appear in annotations

8. 8
Example semantic annotation

9. 9
RDF annotation about
a web resource
chimpanzee
scratching
the head
young
ape08.jpg
active
agent
posture
life stage
Species
ontology
WordNet
ICONCLASS

10. 10
Ontologies describes the concepts
used
great ape
grass landsrain forest
Africa
chimpanzee
geographical
range
subClassOf
typical
habitat

11. 11
Use of semantic markup in
query interfaces

12. 12

13. 13
Annotating with a concept:
term disambiguation

14. 14
W3C’s Semantic Web Activity
 Started in March 2001
• Follow-up of Metadata activity
 RDF Core Working Group
• Revision of RDF and RDF Schema
 Web Ontology Working Group
• Started November 1, 2001
• 50+ members
– HP, IBM, Lucent, Daimler Chrysler, Fujitsu, Intel, Sun, EDS,
Motorola, Nokia, Philips, Unisys, ….
 All proceedings are public
• See http://www.w3.org under “Semantic Web”

15. 15
RDF and RDF Schema
 RDF
• Baseline representation for annotations of web
resources
• Simple triple format
• Already many tools and used in browsers such as
Mozilla
 RDF Schema
• Base-level specification of semantics
• Language constructs include: class, property,
subclass subproperty
• Classes and properties are themselves also
resources: enables annotations about annotations

16. 16
The Web Ontology Language OWL
 OWL adds expressivity to RDF Schema to
enable more powerful semantics:
• cardinality restrictions, local range constraints,
equality of resources, inverse, symmetric and
transitive properties, boolean class combinations,
disjointness and completeness
 OWL Lite: subset of features that is easy to
implement and use
 OWL DL: subset of features supporting
description-logic reasoning (e.g. useful for
ontology construction)

17. 17
OWL documents
Published:
• Requirements document
• OWL Guide (language walkthrough)
• OWL Feature synopsis
• OWL Reference
• OWL Semantics
• OWL Test cases
In preparation:
• UML and XML presentation syntax

18. 18
Moving to the future of the web
Semantic Web LayerCake (Berners-Lee, 99;Swartz-Hendler, 2001)

19. 19
Web services require ontologies
Source: the Web (can’t find it anymore)

20. 20
Use semantics for
service composition
Translate my symptoms from
French and find me a pharmacy
that has the necessary medicine
(then compute how to get there
and print the directions)
Print the directions to a pharmacy
which has a medicine that cures
the symptoms that I will tell you
(in French)

21. 21
Services need web logics

22. 22
Will the Semantic Web succeed?
 One big plus: there is a growing need for
semantic search of information
 Availability of large amounts of semantic
content is essential
• There is a lot of content already out there.
 First applications are likely to be in area of
large virtual collections
• E.g., cultural heritage, medicine
 Web services will not work without ontologies