1 / 23

Ontologies for the Semantic Web

Ontologies for the Semantic Web. Michael Lutz michael.lutz@jrc.it Slides based on Co-ode OWL Tutorial (University of Manchester) http://co-ode.man.ac.uk/resources/tutorials/intro/slides/. Overview. Why do we need ontologies and the Semantic Web? What are ontologies ontology definitions

lenore
Télécharger la présentation

Ontologies for the Semantic Web

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ontologies for the Semantic Web Michael Lutz michael.lutz@jrc.it Slides based on Co-ode OWL Tutorial (University of Manchester)http://co-ode.man.ac.uk/resources/tutorials/intro/slides/ Semantics and Ontologies in GI Services

  2. Overview • Why do we need ontologies and the Semantic Web? • What are ontologies • ontology definitions • properties • Ontology languages • OWL & Description Logics • Reasoning Semantics and Ontologies in GI Services

  3. Impossible (?) using the Syntactic Web… • Complex queries involving background knowledge • Find information about “animals that use sonarbut are not either bats or dolphins”, e.g., Barn owl • Locating information in data repositories • Travel enquiries • Prices of goods and services • Finding and using web services • Visualise surface interactions between two proteins • Delegating complex tasks to web agents • Book me a holiday next weekend somewherewarm, not too far away, and where they speakFrench or English Semantics and Ontologies in GI Services

  4. What is the Problem? Consider a typical web page: • Markup consists of: • rendering information (e.g., font size and colour) • Hyper-links to related content • Semantic content is accessible to humans but not (easily) to computers… Semantics and Ontologies in GI Services

  5. What information can we see… • WWW2002 • The eleventh international world wide web conference • Sheraton waikiki hotel, Honolulu, hawaii, USA, 7-11 may 2002 • 1 location. 5 days. learn. interact • Registered participants coming from: australia, canada, chile denmark, france, germany, … • Register now • On the 7th May Honolulu will provide the backdrop of the eleventh international world wide web conference. This prestigious event … • Speakers confirmed • Tim Berners-Lee (Tim is the well known inventor of the Web, …) • … Semantics and Ontologies in GI Services

  6. What information can a machine see… WWW2002 The eleventh international world wide web conference Sheraton waikiki hotel, Honolulu, hawaii, USA 7-11 may 2002 1 location 5 days learn interact Registered participants coming from australia, canada, chile denmark, france, germany, ghana, hong kong, india, ireland, italy, japan, malta, new zealand, the netherlands, norway, singapore, switzerland, the united kingdom, the united states, vietnam, zaire Register now On the 7th May Honolulu will provide the backdrop of the eleventh international world wide web conference. This prestigious event … Speakers confirmed Tim berners-lee Tim is the well known inventor of the Web, … Ian Foster Ian is the pioneer of the Grid, the next generation internet … Semantics and Ontologies in GI Services

  7. XML markup with “meaningful” tagsThe Solution? <name>WWW2002The eleventh international world wide webcon</name> <location>Sheraton waikiki hotel Honolulu, hawaii, USA</location> <date>7-11 may 2002</date> <slogan>1 location 5 days learn interact</slogan> <participants>Registered participants coming fromaustralia, canada, chile denmark, france, germany, ghana, hong kong, india, ireland, italy, japan, malta, new zealand, the netherlands, norway, singapore, switzerland, the united kingdom, the united states, vietnam, zaire</participants> <introduction>Register nowOn the 7th May Honolulu will provide the backdrop of the eleventh international world wide web conference. This prestigious event …Speakers confirmed</introduction> <speaker>Tim berners-lee</speaker> <bio>Tim is the well known inventor of theWeb,</bio>… Semantics and Ontologies in GI Services

  8. Machine sees… <name>WWW2002The eleventh international world wide webcon</name> <location>Sheraton waikiki hotel Honolulu, hawaii, USA</location> <date>7-11 may 2002</date> <slogan>1 location 5 days…</slogan> <participants>Registered participants coming fromaustralia, canada, chile denmark, france, germany, ghana, hong kong, india, ireland, italy, japan, malta, new zealand, the netherlands, norway, singapore, switzerland, the united kingdom, the united states, …</participants> <introduction>Register nowOn the 7th May Honolulu will provide the backdrop of the eleventh international world wide web conference. This prestigious event …Speakers confirmed</introduction> <speaker>Tim berners-lee</speaker> <bio>Tim is the well known inventor of theWeb,</bio>… Semantics and Ontologies in GI Services

  9. Need to Add “Semantics” • Externalagreement on meaning of annotations • e.g., Dublin Core: agree on the meaning of a set of annotation tags • but this approach is inflexible and only a limited number of things can be expressed • Use ontologies to specify meaning of annotations • Ontologies provide a vocabulary of terms • New terms can be formed by combining existing ones • Meaning (semantics) of such terms is formally specified • Can also specify relationships between termsin multiple ontologies Semantics and Ontologies in GI Services

  10. Ontology in Computer Science • An ontology is an engineering artifact: • constituted by a specific vocabulary used to describe a certain reality, plus • a set of explicit assumptions regarding the intended meaning of the vocabulary. • Thus, an ontology describes a formal specification of a certain domain: • Shared understanding of a domain of interest • Formal and machine manipulable model of a domain of interest “An explicit specification of a conceptualisation” [Gruber93] Semantics and Ontologies in GI Services

  11. Ontology Components • Names for important concepts in the domain • Elephant is a concept whose members are a kind of animal • Herbivore is a concept whose members are exactly those animals who eat only plants or parts of plants • Background knowledge/constraints on the domain • Adult_Elephants weigh at least 2,000 kg • All Elephants are either African_Elephants or Indian_Elephants • No individual can be both a Herbivore anda Carnivore Semantics and Ontologies in GI Services

  12. Pump: “a device for moving a gas or liquid from one place or container to another” (pump has (superclasses (…)) Semantics hardwired; used at runtime Semantics processed and used at runtime Text descriptions Informal (explicit) Formal (for humans) Formal (for machines) A semantic continuum [Mike Uschold, Boeing Corp] Shared human consensus Implicit  Further to the right  • Less ambiguity • Better interoperation • More robust – less hardwiring • More difficult Semantics and Ontologies in GI Services

  13. Ontology Design and Deployment • In the Semantic Web there should be tools and services to help users: • Design and maintain high quality ontologies • Store (large numbers) of instances of ontology classes, e.g. annotations from web pages • Answer queries over ontology classes and instances, e.g. • Find more general/specific classes • Retrieve annotations/pages matching a given description • Integrate and align multiple ontologies Semantics and Ontologies in GI Services

  14. Why Ontology Engineering is hard… • Clash of intuitions: Domain Experts vs. Logicians • Transparency & predictability vs. Rigour & Completeness • Neophytes caught in the muddled middle • The knowledge acquisition “bottleneck” • Assuring quality & managing change • Confusion of terminology and usage • Interdisciplinarity: Linguistics, Cognitive science, Software engineering, Philosophy • A jumble of syntaxes Semantics and Ontologies in GI Services

  15. Vocabulary • “Class”  “Concept”  “Category”  “Type” • are often used synonymously, but more precisely… • categories are in the world • concepts are in the mind • classes/types are in the ontology • “Instance”  “Individual” • “Entity”  “object” • can be class or individual • “Property”  “Slot”  “Relation”  “Relationtype”  “Attribute”  Semantic link type”  “Role” Semantics and Ontologies in GI Services

  16. Domain-independent applications An Ontology should be just the Beginning Databases Declare structure Ontologies Knowledge bases The “SemanticWeb” Provide domain description Software agents Problem-solving methods Semantics and Ontologies in GI Services

  17. Ontology Languages • Wide variety of languages for “Explicit Specification” • Graphical notations, e.g. UML, Semantic networks, Topic Maps (see http://www.topicmaps.org/), RDF • Logic based, e.g. Description Logics (e.g., OWL), Rules (e.g., RuleML, LP/Prolog), First Order Logic (e.g., KIF), Conceptual graphs, higher order and non-classical logics • Probabilistic/fuzzy • Degree of formality varies widely • Increased formality makes languages more amenableto machine processing(e.g., automated reasoning) Semantics and Ontologies in GI Services

  18. Language Primitives • Objects/Instances/Individuals • Elements of the domain of discourse • Equivalent to constants in FOL • Types/Classes/Concepts • Sets of objects sharing certain characteristics • Equivalent to unary predicates in FOL • Relations/Properties/Roles • Sets of pairs (tuples) of objects • Equivalent to binary predicates in FOL Semantics and Ontologies in GI Services

  19. Web Ontology Language Requirements • Desirable features for Web Ontology Language: • Extends existing Web standards, e.g. XML, RDF, RDFS • Easy to understand and use  should be based on familiar KR idioms • Formally specified • Of “adequate” expressive power • Possible to provide automated reasoning support Semantics and Ontologies in GI Services

  20. OWL Language • Three species of OWL • OWL full is union of OWL syntax and RDF • OWL DL restricted to FOL fragment ( DAML+OIL) • OWL Lite is “easier to implement” subset of OWL DL • OWL DL based on SHIQDescription Logic • OWL DL benefits from many years of DL research • Well defined semantics • Formal properties well understood (complexity, decidability) • Known reasoning algorithms • Implemented systems (highly optimised) Semantics and Ontologies in GI Services

  21. ??? ??? ??? (In)famous “Layer Cake”  Semantics+reasoning ?  Relational Data ?  Data Exchange TimBL, 2000 (http://www.w3.org/2000/ Talks/1206-xml2k-tbl/slide10-0.html) Semantics and Ontologies in GI Services

  22. References • Daconta, M.C., Obrst, L.J. & Smith, K.T. (2003): The Semantic Web. A Guide to the Future of XML, Web Services, and Knowledge Management, John Wiley & Sons • esp. chapter 8: Understanding Ontologies • McGuinness, D.L. & van Harmelen, F. (Eds.) (2004): OWL Web Ontology Language Overview, available from http://www.w3.org/TR/owl-features/ • Baader, F., Calvanese, D., McGuinness, D., Nardi, D. & Patel-Schneider, P. (2003): The Description Logic Handbook, Cambridge University Press • esp. introductory chapters 1 & 2 Semantics and Ontologies in GI Services

  23. Questions??? Semantics and Ontologies in GI Services

More Related