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Semantic Web - Ontologies

This document provides an in-depth overview of ontologies in the context of the Semantic Web, illustrating their philosophical roots and practical applications. It defines ontologies as formal specifications for conceptual understandings, emphasizing their role in enhancing communication and interoperability across disparate systems. Key components such as taxonomies, inference rules, and ontology engineering processes, including languages like XML and HTML-based representation, are discussed. Relevant tools for creating ontologies, such as Protégé and WebOnto, are also highlighted.

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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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