Semantic Web: From Representations to Applications
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Transcript of Semantic Web: From Representations to Applications
Semantic Web: From Representations to Applications
Guus SchreiberFree University AmsterdamCo-chair W3C Web Ontology Working GroupCo-chair W3C Semantic Web Best Practices
and Deployment Working Group
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
Disclaimer
This presentation describes work of many different people, including many participating in respective W3C Working Groups as well as others
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
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
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
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?
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.
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
Is RDF/OWL just another datamodelling/KR language?
Key differences: All classes/properties/individuals have a URI as
identifier RDF/XML exchange syntax enables
interoperabilityXML 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
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)
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”
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
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
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>
OWL abstract syntax
Used in a (very) sloppy fashion in this presentation
Developed for specifying the OWL DL semantics
UML Profile for OWL Under
development at OMG
Not trivial, e.g. RDF/OWL properties are different from UML associations
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#>.
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
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/
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/
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)
Representing a numeric constraintthrough a datatypeClass(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
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
RDF in XHTML
How to mark up your (X)HTML page? Various proposals under discussion in
RDF-in-XHTML Task Forcehttp://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2004Oct/
Link typing using “rel” attribute?! Consequences for HTTP GET?!
Other work (planned) in the W3C Best Practices WG: a selection
Tutorial pagehttp://www.w3.org/2001/sw/BestPractices/Tutorials
Tools page May just build on work of others, e.g. see DAML
tool-assessment studyhttp://semwebcentral.org/
Publication of vocabularies/ontologies WordNet is first on the list Units and measures is likely next target
Links to MPEG, Topic Maps
Applications and demo’s
Webloghttp://esw.w3.org/mt/esw/archives/cat_applications_and_demos.html
Four examples1. AKTive Space: CS research in the UK2. DOPE: Drug Ontology Project at Elsevier3. Building Finder (USC)4. Finnish Museums on the Web
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
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
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
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
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.
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
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
More information
See home page of the Best Practices WG:
http://www.w3.org/2001/sw/BestPractices/
All proceedings are public
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