Knowledge Representation on the Semantic Web by

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Knowledge Representation on the Semantic Webby

• Femi G. Olumofin
• Department of Computer Science
• University of Manitoba,
• Winnipeg, Canada
• March 8, 2004

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Outline

• Introduction
• The Semantic Web Layers
• Resource Description Framework (RDF)
• Ontology
• OWL Web Ontology Language
• Semantic Web Current Activity
• Conclusion

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Introduction The Current Web

• The current Web represents knowledge as a global
  repository of resources interconnected by
  hyperlinks (href).
• Accessed by specifying URI addresses, searching,
  and following links to find other related
  resources 1

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Introduction The Current Web

• Human do the difficult part
• Linking, and
• interpreting
• Machines do the easy part
• Presentation (of requested resource)
• Humans can interpret because we know the meaning
  (or semantics) of web contents
• If we add semantic annotations to web resources,
  then machines would be able to interpret!
• Syntactic Web -gt Semantic Web

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Introduction The Vision of the Semantic Web

• To develop facilities (enabling standards and
  technologies) to express information on the Web
  in a form that can be shared and processed by
  machines and human
• The Semantic Web is a web of data, in some ways
  like a global database 2.

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Introduction What is the Semantic Web?

• Definition The Semantic Web provides a common
  framework that allows data to be shared and
  reused across application, enterprise, and
  community boundaries. It is a collaborative
  effort led by W3C with participation from a large
  number of researchers and industrial partners. It
  is based on the Resource Description Framework
  (RDF), which integrates a variety of applications
  using XML for syntax and URIs for naming. 10.
• "The Semantic Web is an extension of the current
  web in which information is given well-defined
  meaning, better enabling computers and people to
  work in cooperation." 3.

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The Semantic Web Layers
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The Resource Description Framework (RDF)

• Provides a base language for representing
  information about web resources
• Provides a common framework for encoding,
  exchange, and reuse of structured metadata (or
  semantic annotation)
• Uses Web identifiers (URI URL, URN) to identify
  resources
• Uses XML for the exchange and processing of
  metadata
• Metadata is machine understandable
• Recently became a W3C Recommendation as of
  February 10, 2004

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The RDF Data Model

• Represents knowledge as statements in the form of
  a directed labeled graph of the triple ltSubject,
  Predicate, Objectgt
• Subject
• Resource An entity a class name or "any
  addressable unit of information or service"16
• Predicate
• Property, attribute, characteristics, verb
• Object
• Value, Literal
• Defines resource in terms of property and value

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The RDF Model - Example

• Represent Tim Berners-Lee is the author of
  Semantic Web Road map at http//www.w3.org/Desig
  nIssues/Semantic
• lt?xml version"1.0"?gt
• ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/22-r
  df-syntax-ns"
• xmlnsexterms" http//purl.org/dc/terms"gt
• ltrdfDescription rdfabout" http//www.w3.org/Des
  ignIssues/Semantic"gt
• ltextermsauthour rdfresourcehttp//www.w3.org/P
  eople/Berners-Lee/gt
• lt/rdfDescriptiongt
• lt/rdfRDFgt

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The RDF Model - Example

• Extend representation to include Tim Berners-Lee
  email timbl _at_ w3.org and address 200
  Technology Square, Cambridge MA 02139

http//www.w3.org/2000/10/swap/pim/contactaddress

http//.../contactmailbox
timbl_at_w3c.org
Address
http//.../contact/addressstreet
http//.../contact/addresscityandstate
200 Technology Square
Cambridge MA 02139
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The Resource Description Framework- Limitations

• RDF provides framework for describing web
  resources using metadata
• Programs can only understand web resources if
  they understand the meaning of the metadata and
  its variations in different RDF descriptions
  (e.g., Personnel vs. Employee, matriculation
  vs. student id, LastName vs. Surname)
• RDF is similar to defining table attributes in
  RDBMS
• External agreement on meaning of annotations for
  a domain is required for interoperability and
  machine understandability

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The Resource Description Framework- Limitations

• The Semantic Web needs support for ontologies.

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Ontology

• Ontology refers to the science of describing the
  kinds of entities in the world and how they are
  related 5
• Ontology provides sources of precisely defined
  knowledge (vocabulary), which can be shared
  across applications and humans.
• An Ontology consists of a hierarchical
  description of important concepts in a domain and
  possible constraints
• An explicit specification of a
  conceptualisation 6

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Ontology Languages for the Semantic Web

• Ontology Language Layer is on top of the Resource
  Description Framework (RDF)
• DAML - DARPA Agent Markup Language
• OIL - Ontology Inference Layer
• DAMLOIL - "semantic markup language for Web
  resources
• OWL - Web Ontology Language (revision of DAMLOIL
  and is based on Description Logics)
• OWL is a recent W3C Recommendation (February
  2004) 7, 8.

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OWL Web Ontology Language

• Designed to enable machine interpretability of
  Web contents (not for human interpretation).
• Three sublanguages of OWL
• OWL Lite supports simple classification hierarchy
  and simple constraints. It is the easiest to
  implement and even provides a quick migration
  path for thesauri and other taxonomies.
• OWL DL offers maximum expressiveness while
  retaining computational completeness and
  decidability. Full formalism of DL supported.
• OWL Full offers maximum expressiveness with full
  syntactic liberty of the RDF without
  computational guarantees.

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OWL Web Ontology Language

• Offers extended vocabulary and a formal semantics
  for defining classes and properties, including
• cardinality (e.g. minCardinality, maxCardinality,
  cardinality)
• equality (e.g. equivalentClass)
• relationships between classes (e.g. disjointWith,
  unionOf)
• characteristics of properties (e.g.
  FunctionalProperty)
• Example Indicate that student has only one
  StudentID

owlClass
rdftype
rdfssubClassOf
StudentID
rdfssubClassOf
owlRestriction
Student
owlonProperty
1
owlcardinality
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OWL Web Ontology Language - Example

• A CS Graduate Student is either in the Masters or
  PhD programme. The Masters programme is made up
  of Course work and Thesis. A student has to take
  at least four courses and the 74.722 course.
• What is the OWL representation for this ontology?

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OWL Web Ontology Language - Example
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W3C Semantic Web Group Current Activity

• W3C Lunched Phase 2 of the Semantic Web Activity!
  February 25, 2004
• Two new Working Groups have been formed.
• Best Practices and Deployment WG focused on
  providing consensus-based guidance - including
  practical deployment recommendations, engineering
  guidelines, ontology / vocabulary development
  practices, educational material and effective
  demonstrations, designed to facilitate Semantic
  Web deployment. 10
• RDF Data Access Working Group Tasked with
  developing an RDF query language (with
  interoperability as SQL did for relational
  databases)
• Activities continue in other Work Groups of the
  Semantic Web RDF Core and Web Ontology WGs, the
  Semantic Web Interest Group, and the Semantic Web
  Coordination Group.

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Conclusion

• The Web can only reach its full potential when
  programs can seamlessly process the vast
  information represented on the World Wide Web
  (WWW).
• The Semantic Web, which is an extension of the
  current Web, is intended to address this need.
• The W3C Semantic Web Activity group is driving
  the Semantic Web through
• A global vision of a Layered architecture of
  standards and technologies that achieves the
  Semantic Web
• Development of frameworks and languages to
  support the semantic annotation of web resources
  and the development of ontologies.
• And recently, provision of pedagogical support
  for seamless adoption of the standards and
  technologies
• Development Tools and Industry solutions are
  already emerging based on the W3C Semantic Web
  Activity Group efforts

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References

• 1 Marja-Riitta Koivunen and Eric Miller, W3C
  Semantic Web Activity. The proceedings of the
  Semantic Web Kick-off Seminar in Finland,
  November 2, 2001
• 2 Tim Berners-Lee, Semantic Web Road map,
  September 1998. Available http//www.w3.org/Desig
  nIssues/Semantic.html
• 3 Tim Berners-Lee, James Hendler, Ora Lassila,
  The Semantic Web, Scientific American, May 2001
  http//www.w3.org/2002/07/swint.
• 4 Eric Miller, Digital Libraries and the
  Semantic Web. Available http//www.w3.org/2001/09
  /06-ecdl/slide17-0.html
• 5 Michael K. Smith, Chris Welty,and Deborah L.
  McGuinness, W3C Recommendation OWL Web Ontology
  Language Guide, February 2004. Available
  http//www.w3.org/TR/owl-guide/
• 6 M. Uschold, M. Gruninger, Ontologies
  Principles, Methods and Applications. Knowledge
  Engineering Review 11(2) (1996).
• 7 Web Ontology Language Home Page
  http//www.w3c.org/2001/sw/WebOnt/
• 8 Christel Kemke, 74.419 Artificial
  Intelligence Course Notes on Semantic Web, 2003
• 9 James Hendler, Tim Berners-Lee, and Eric
  Miller. Integrating Applications on the Semantic
  Web, Journal of the Institute of Electrical
  Engineers of Japan, Vol 122(10), October, 2002,
  p. 676-680. Available http//www.w3.org/2002/07/s
  wint
• 10 Semantic Web Home Page http//www.w3.org/2001
  /sw/
• 11 RDF Home Page http//www.w3.org/RDF/
• 12 Web Ontology Language Home Page
  http//www.w3c.org/2001/sw/WebOnt/
• 13 Description Logics Home Page
  http//dl.kr.org/
• 14 DAML Home Page http//www.daml.org/
• 15 OIL Home Page http//www.ontoknowledge.org/oi
  l/
• 16 W3C Home Page http//www.w3c.org/

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QA
Thank You!