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Semantic Web - Ontologies

Semantic Web - Ontologies. Sameer Totey. What is Ontology. Branch of Philosophy that studies nature of existence Specification of a conceptualization Document or file that formally defines relations among terms Shared understanding of some domain of interest. What is Ontology for Web ?.

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Semantic Web - Ontologies

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  1. Semantic Web - Ontologies Sameer Totey CSCI 7818 - Web Infrastructure, Services, and Applications

  2. What is Ontology • Branch of Philosophy that studies nature of existence • Specification of a conceptualization • Document or file that formally defines relations among terms • Shared understanding of some domain of interest CSCI 7818 - Web Infrastructure, Services, and Applications

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  5. What is Ontology for Web ? • A Taxonomy which defines classes of objects and relations among them • A set of inference rules • (Classes subclasses and relations among entities) CSCI 7818 - Web Infrastructure, Services, and Applications

  6. Lack of a shared understanding leads to poor communication Disparate modeling paradigms, languages and software tools limit Interoperability Knowledge Sharing and reuse Why Ontologies? CSCI 7818 - Web Infrastructure, Services, and Applications

  7. Theory • Usually Ontology structure is represented as a 5 Tuple O = (C,R, H, rel, A) • Disjoint Sets C and R are concept identifiers and relation identifiers respectively • H is the concept hierarchy. Also called Taxonomy. H(C1,C2) means C1 is subconcept of C2. H is a directed transitive relation. • Rel is a function that relates concept non-taxonomically, rel : R  C X C • A is a set of ontology Axioms, expressed in an logical language like first order logic. CSCI 7818 - Web Infrastructure, Services, and Applications

  8. Ontology Engineering • The task of developing an ontology is a typical knowledge acquisition task involving • Kickoff • Refinement • Evaluation • Maintenance CSCI 7818 - Web Infrastructure, Services, and Applications

  9. Languages • There are several representation languages in the AI (machine learning, natural language processing, knowledge representation etc) community based on FOL like • Frame Logic • Loom • Ontololingua etc. • Web needs XML based language : defining a language on top of XML syntax • SHOE (SHOE is an HTML-based knowledge representation language) Simple HTML Ontology Extention. • XOL (Ontology Exchange Language) • OML (Ontology markup language) • RDFS (Resourse description framework scheme language) • OIL (Ontology Interchange Language) • DAML (DARPA Agent markup language) CSCI 7818 - Web Infrastructure, Services, and Applications

  10. Editors • Tools that help create ontologies and metadata that can be used by multiple agents: • Protégé • WebOnto • OilEd • ONTOEdit CSCI 7818 - Web Infrastructure, Services, and Applications

  11. Related issues: • Higher order logic based inference engines – Needed but not feasible • First order logic based inference engines – feasible but limited expressive power, FOL is semi-decidable some inferences are computationally intractable • Interoperability • Bremer Semantic Translation project • SKC (Stanford Scalable Knowledge Composition) project CSCI 7818 - Web Infrastructure, Services, and Applications

  12. References • http://www.fzi.de/wim [Development and applications of Ontologies] tutorial • www.sematicweb.org • www.ontologyworks.com CSCI 7818 - Web Infrastructure, Services, and Applications

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