Natural Language and Speech Processing Professor: Dr. Christel Kemke Winter 2004 Knowledge Representation on the Semantic Web by Femi G. Olumofin Department of Computer Science University of Manitoba, Winnipeg, Canada March 8, 2004

Friday, April 17, Outline Introduction The Semantic Web Layers Resource Description Framework (RDF) Ontology OWL Web Ontology Language Semantic Web Current Activity Conclusion

Friday, April 17, 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]

Friday, April 17, 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 -> Semantic Web

Friday, April 17, 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].

Friday, April 17, 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].

Friday, April 17, The Semantic Web Layers RDF-basedXML for syntax URI for naming Research Issues OWL (W3C Recommendation since February, 2004), OIL, DAML

Friday, April 17, 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

Friday, April 17, The RDF Data Model Represents knowledge as statements in the form of a directed labeled graph of the triple 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 Predicate Subject Object

Friday, April 17, The RDF Model - Example Represent “Tim Berners-Lee is the author of ‘Semantic Web Road map’ at <rdf:RDF xmlns:rdf=" xmlns:exterms=" Statement Property Resourc e Value

Friday, April 17, The RDF Model - Example Extend representation to include “Tim Berners-Lee w3.org] and address [200 Technology Square, Cambridge MA 02139] Address 200 Technology SquareCambridge MA

Friday, April 17, 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

Friday, April 17, The Resource Description Framework- Limitations The Semantic Web needs support for ontologies.

Friday, April 17, 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]

Friday, April 17, 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 DAML+OIL - "semantic markup language for Web resources“ OWL - Web Ontology Language (revision of DAML+OIL and is based on Description Logics) OWL is a recent W3C Recommendation (February 2004) [7, 8].

Friday, April 17, 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. OWL Full OWL DL OWL Lite RDF, etc.

Friday, April 17, 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 rdfs:subClassOf #Student owl:Restriction #StudentID 1 owl:Class owl:cardinality owl:onProperty rdfs:subClassOf rdf:type

Friday, April 17, 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 course. What is the OWL representation for this ontology?

Friday, April 17, OWL Web Ontology Language - Example

Friday, April 17, 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.

Friday, April 17, 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

Friday, April 17, 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 Available: [3] Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web, Scientific American, May [4] Eric Miller, Digital Libraries and the Semantic Web. Available: ecdl/slide17-0.html [5] Michael K. Smith, Chris Welty,and Deborah L. McGuinness, W3C Recommendation: OWL Web Ontology Language Guide, February Available: [6] M. Uschold, M. Gruninger, Ontologies: Principles, Methods and Applications. Knowledge Engineering Review 11(2) (1996). [7] Web Ontology Language Home Page [8] Christel Kemke, 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 Available: [10] Semantic Web Home Page [11] RDF Home Page [12] Web Ontology Language Home Page [13] Description Logics Home Page [14] DAML Home Page [15] OIL Home Page [16] W3C Home Page

Friday, April 17, Q&A