The Semantic Web:Status and Prospects

Guus Schreiber

University of Amsterdam

Co-chair W3C Web Ontology Working Group

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The Evolving Web

Web ofKnowledge

HyperText Markup LanguageHyperText Transfer Protocol

Resource Description FrameworkeXtensible Markup Language Self-Describing Documents

Foundation of the Current Web

Proof, Logic andOntology Languages Shared terms/terminology

Machine-Machine communication

1990

2000

2010

Berners-Lee, Hendler; Nature, 2001

DOCUMENTS

DATA/PROGRAMS

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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

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W3C’s view on Web Semantics

Semantic Web LayerCake (Berners-Lee, 99;Swartz-Hendler, 2001)

Semantic web languages provide “external” referents for XML documents

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SW languages add mappingsAnd structure.

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What is an Ontology?

In philosophy: theory of what exists in the world

In IT: consensual & formal description consensual & 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 in Ontology = key technology in semantic information processingsemantic information processing

– Applications: knowledge management, e-business, industrial engineering, semantic world-wide web

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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

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Example semantic annotation

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RDF annotation about a web resource

chimpanzee

scratchingthe head

youngape08.jpg

activeagent

posture

life stage

Speciesontology

WordNet

ICONCLASS

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Ontologies describes the concepts used

great ape

grass landsrain forest

Africa

chimpanzee

geographicalrange

subClassOf

typicalhabitat

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Use of semantic markup in query interfaces

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Annotating with a concept:term disambiguation

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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”

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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

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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)

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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

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Moving to the future of the web

Semantic Web LayerCake (Berners-Lee, 99;Swartz-Hendler, 2001)

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Web services require ontologies

Source: the Web (can’t find it anymore)

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Use semantics for service composition

Translate my symptoms fromFrench and find me a pharmacythat has the necessary medicine(then compute how to get thereand print the directions)

Print the directions to a pharmacywhich has a medicine that curesthe symptoms that I will tell you (in French)

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Services need web logics

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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