This document discusses semantic web representations and applications. It provides an overview of the W3C Web Ontology Working Group and Semantic Web Best Practices and Deployment Working Group, including their goals and key issues addressed. Examples of semantic web applications are also described, such as using ontologies to integrate information from heterogeneous cultural heritage sources.

1. Semantic Web: From
Representations to Applications
Guus Schreiber
Free University Amsterdam
Co-chair W3C Web Ontology Working Group
Co-chair W3C Semantic Web Best Practices
and Deployment Working Group

2. Overview
 Representations:
 Reflections on the making of OWL and its
relation to RDF
 Using representations
 Best practices (as far as we know then
now) to help application developers
 Applications
 Examples from the SWBPD weblog

3. Disclaimer
 This presentation describes work of
many different people, including
many participating in respective W3C
Working Groups as well as others

4. W3C Web Ontology Working Group
 Chartered to develop the Ontology
Vocabulary for the Semantic Web.
 Starting point: DAML+OIL
 Started in November 2001
 Factions:
 logicians (Description Logic, KIF)
 knowledge/ontology engineers
 RDF developers
 OWL Recommendation published 10
February 2004

5. Working group communication
 Mailing lists
 working-group list: 8,000 messages in two years
 public comments list: 600 messages in 18
months
 Telecons
 60 telecons of 60-90 minutes with 10-30 people
 simultaneous scribing in IRC (chat) channel
 Face-to-face meetings
 five two-day meetings during first 15 months
 All proceedings in the public domain:
http://www.w3.org/2001/sw/WebOnt

6. Key issue to be resolved:
5.3 Semantic Layering
 OWL is expected to
be semantically
compatible with
RDF(S).
 Problems were
foreseen with
aligning a DL-style
model theory with
the RDF model
theory

7. The Semantic Layering debate
 Excerpt from a telecon debate:
"You are not creating a semantic web, but
semantic islands with high fences"
"But your are creating a semantic swamp,
with crocodiles and snakes"
 What do you prefer?

8. Consensus on Semantic Layering
 OWL Full ("Large OWL", "Great Horned OWL")
 Free mixing of OWL and RDF = high expressivity
 Non-standard formalization
 Tractability not guaranteed
 OWL DL ("Fast OWL")
 Maximize expressiveness while retaining tractability
 Standard formalization
 Same language constructs as OWL Full
 Constraints on RDF/OWL vocabulary use
 Correspondence theorem links the two styles of
semantics: entailments in OWL DL also hold in OWL
Full.

9. RDF/OWL schema constructs
 RDFS Schema
 (sub)classes, (sub)properties, domain, range,
datatypes (using XML Schema)
 OWL Lite
 cardinality 0/1, local property restrictions,
inverse/transitive/symmetric properties,
(in)equality of classes/instances
 OWL DL
 enumeration, disjunction, conjunction, negation,
hasValue
 OWL Full
 meta-modeling

10. Is RDF/OWL just another
datamodelling/KR language?
Key differences:
 All classes/properties/individuals have a URI as
identifier
 RDF/XML exchange syntax enables
interoperability
XML features
 UTF-8 character set
 Support for multilinguality
 Use of XML Schema datatypes: numeric, date,
time, etc.
For the rest: RDF/OWL is state-of-the-art
concept language

11. Semantic Web Best Practices and
Deployment Working Group
 Started 1 March 2004 => early days
 Co-chairs David Wood and Guus Schreiber
 30+ participants
 Objective: support for semantic-web
application developer
 Focus on “low hanging fruit”
 Publication of key ontologies/vocabularies,
development guidelines, ontology-design
patterns, repositories, links to related
techniques, ……
 High expectations, not much effort (yet)

12. Issues for publishing ontologies:
good and bad ontologies?!
 Good ontologies are used
 Good ontologies represent some form
of consensus in a community
 Good ontologies are maintained
 Good ontologies do not need to be
complex
 Good ontologies may contain
“mistakes”

13. ontology = community consensus
N.B.
It is a contradiction
in terms to talk
about “creating my
own ontology”!
Source: Financial Times,
e-procurement, Oct. 2000

14. Thesauri and ontologies
 ISWC’03 Semantic Web Challenge
showed that thesauri are important
resources for SW applications
 Typically weak semantic structure
 Approach in Best Practices WG:
 Phase 1: “as-is” conversion
 Phase 2: additional ontological
interpretations/extensions

15. Human-readable syntax?!
<owl:Class rdf:ID="MozartDaPonteOpera">
<owl:equivalentClass>
<owl:Class>
<owl:oneOf rdf:parseType="Collection">
<Opera rdf:about="#NozzDiFigaro"/>
<Opera rdf:about="#DonGiovanni"/>
<Opera rdf:about="#CosiFanTutte"/>
</owl:oneOf>
</owl:Class>
</owl:equivalentClass>
</owl:Class>

16. OWL abstract syntax
 Used in a (very) sloppy fashion in this
presentation
 Developed for specifying the OWL DL
semantics

17. UML Profile for OWL
 Under
development at
OMG
 Not trivial, e.g.
RDF/OWL
properties are
different from
UML associations

18. N3 Turtle syntax
 See note by Dave Beckett (Bristol)
:pressureInHg a owl:ObjectProperty;
rdfs:domain :DiastolicBloodPressure;
rdfs:range xsd:nonNegativeInteger.
@prefix owl:
<http://www.w3.org/2002/07/owl#>.
@prefix xsd:
<http://www.w3.org/2001/XMLSchema#>.

19. Ontology engineering patterns
 Best practices for frequently occurring
modeling problems
 WG documents outline alternatives with
pros and cons
 Currently three notes published:
 Classes as values
 N-ary relations
 Specification of value sets
 Planned:
 Part-of, numeric constraints, QCRs

20. Representing value sets
 Intuitive representation of color value set:
class/datatype color
with instances/values “red”, “white”, etc.
 But suppose we want to talk about a subtype of
“red”, e.g. “vermillion red”
 Pattern:
 Represent values as subclass hierarchy of value type
 This preserves flexibility
 Use anonymous instances as property values
“This porcelain vase has as color some value of vermillion
red”
 See note by Alan Rector
http://www.w3.org/TR/swbp-specified-values/

21. Classes as values
 Common problem when using a hierarchy
of concepts for indexing purposes
 Example: indexing books with concepts
from the ACM computer-science subject
hierarchy
 See draft technical note by Noy:
 Four options with different merits
 See note by Natasha Noy:
http://www.w3.org/TR/swbp-classes-as-values/

22. Numeric constraints and user-
defined XML Schema datatypes
 Example: “an elevated diastolic blood
pressure is a diastolic blood pressure of 90
Hg or more”
 Currently no simple way to represent this in
OWL
 User-defined XML Schema datatypes could
provide a solution
 Currently not possible for detailed technical
reasons
 SWBPD task force is active in trying to
solve this problem (Jeremy Carroll, HP)

23. Representing a numeric constraint
through a datatype
Class(DiastolicBloodPressure)
Propert(pressureInHg
domain(DiastolicBloodPressure)
range(xsd:nonNegativeInteger))
Class(ElevatedDiastolicBloodPressure
subClassOf(DiastolicBloodPressure)
subClassOf(Restriction
onProperty(pressureInHg)
allValuesFrom(ex:NinetyPlus))
Plus corresponding definition for the
ex:NinetyPlus user-defined datatype

24. Pervasive issue: metamodelling
 OWL DL requires strict separation of
classes and instances
 But on the Semantic Web my
instances may be your classes!
 Metamodelling features especially
required in vocabulary/ontology
mapping and/or interpretation
 Cf. Protégé metamodelling facilities

25. RDF in XHTML
 How to mark up your (X)HTML page?
 Various proposals under discussion in
RDF-in-XHTML Task Force
http://lists.w3.org/Archives/Public/public-rdf-in-xht
 Link typing using “rel” attribute?!
 Consequences for HTTP GET?!

26. Other work (planned) in the W3C
Best Practices WG: a selection
 Tutorial page
http://www.w3.org/2001/sw/BestPractices/Tutorials
 Tools page
 May just build on work of others, e.g. see DAML
tool-assessment study
http://semwebcentral.org/
 Publication of vocabularies/ontologies
 WordNet is first on the list
 Units and measures is likely next target
 Links to MPEG, Topic Maps

27. Applications and demo’s
 Weblog
http://esw.w3.org/mt/esw/archives/cat_application
 Four examples
1. AKTive Space: CS research in the UK
2. DOPE: Drug Ontology Project at Elsevier
3. Building Finder (USC)
4. Finnish Museums on the Web

28. AKTive Space
 AKT project (Shadbolt et al. ), winner
Semantic Web Challenge 2003)
 Integration of heterogeneous sources
 Papers, researchers, projects
 430 Mb in total
 RDF/OWL used for syntactic interoperability
 Storage/access issues
 Schema mapping is required
 Referential integrity is a problem
 Use of owl:sameAs
 Use automatic techniques in combination with
user approval

30. DOPE: thesaurus-based search of
large document repositories
 Stuckerschmidt et al. (2003)
 EMTREE thesaurus (MesSH-based)
 Documents
 5M Medline abstracts
 500K full-text articles of Elsevier
 Automatic document indexing
 RDF used for syntactic interoperability
 RDF wrapper for SOAP-based access to documents
 Disambiguation of search terms
 Visualization of search results through semantic
categories
 Needed to prevent information overflow

32. Building Finder: integrating image
analysis and textual sources
 Knoblock et al. (USC/ISI)
 Multiple heterogeneous sources
 Satellite images (Microsoft Terraservice)
 Road map info (US)
 Address information (white pages)
 Image analysis techniques to map
satellite data to road map
 RDF used for syntactic interoperability

34. Finnish Museums on the
Semantic Web
 Hyvonen et al. (2004)
 Multiple museum collections
 Indexed with multiple ontologies
 Artifact, material, actor, location, time,
event
 RDF used for syntactic interoperability
 Ontologies used for query
specialization/generalization

36. Cultural heritage collections:
possible use case
 A person is interested
in Fauve paintings
 There is a digital
collection with images
of paintings of Andre
Derain
 The Derain images
match the query,
despite the fact that
“Fauve does not appear
in the annotation.

38. Application issues (1)
 Public domains are promising application
areas
 Medicine, cultural heritage, digital libraries
 Many existing vocabularies & annotations
 Application-pull
 Information integration/presentation is
prime use case
 Multimedia is important focus
 Requires multi-disciplinary approach

39. Application issues (2)
 Free access to vocabularies /
ontologies is a real problem
 AAT, EuroWordNet
 Similar applications can be built for
company intranets
 NOTE for academics: be conscious of
unfair criticism of application papers

40. More information
See home page of the Best Practices
WG:
http://www.w3.org/2001/sw/BestPractices/
All proceedings are public

41. Related European effort:
IST Knowledge Web network
 http://knowledgeweb.semanticweb.org
 Objectives (selection):
 Research integration
 Summer schools
 Educational material
 Showcase applications
 Industrial dissemination
 Started 1-1-2004 and runs for four years