Keynote, XML days, van Humboldt University, Berlin, 2004

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