1. Ontologies and the Semantic Web by Ian Horrocks presented by Thomas Packer 1

2. Overview The current web is simple and usable. More could be done to build more intelligent tools (agents). Doing this requires solving hard problems: – Knowledge representation and reasoning – Natural language processing – Computer vision – Agent systems “My aim here is to show here that even if a full realization of the Semantic Web is still a long way off, Semantic Web technologies already have an important influence on the development of information technology.” 2

3. Challenges Natural language: – Page says “Harry Potter has a pet named Hedwig.” – Search for pages about wizards owning raptors. – Solution: interpret and represent in machine readable format. Distributed information: – Ask a question whose answer is not found on one page. – Solution: Integrate facts in integratable formats. 3

4. Set of RDF Triples = RDF Graph 4

5. Challenge Solved Page says “Harry Potter has a pet named Hedwig.” Search for pages about wizards owning raptors. 5

6. OWL and Class Definitions Extensional Definition Intensional Definition 6

7. Use of Description Logic in OWL Ontologies Infer new facts – Unlike databases with a closed-world assumption (e.g. unasserted information is assumed false) Temporary inconsistency allowed – Unlike database that prevent assertions that violate constraints (e.g. unique names) Warnings in a ontology development environment to guide debugging. 7

8. Conclusion OWL and RDF are good tools, particularly in applications where – Information has high value – The schema plays an important role – Information may be incomplete They are working on making it more expressive (OWL 2 and SWRL), scalable and modular. Will be more useful as more people use them and provide tools for working with them. Our research could make use of existing knowledge, plus reasoning, to do better information extraction from web pages. 8

9. Questions 9