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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 ?. - PowerPoint PPT Presentation
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04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications
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Semantic Web - Ontologies
Sameer Totey
04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications
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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
04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications
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Acrobat Document
04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications
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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)
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Lack of a shared understanding leads to poor communication
Disparate modeling paradigms, languages and software tools limit
1. Interoperability
2. Knowledge Sharing and reuse
Why Ontologies?
04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications
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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.
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Ontology Engineering
The task of developing an ontology is a typical knowledge acquisition task involving
1. Kickoff
2. Refinement
3. Evaluation
4. Maintenance
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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)
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Editors
Tools that help create ontologies and metadata that can be used by multiple agents: Protégé WebOnto OilEd ONTOEdit
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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
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References
http://www.fzi.de/wim [Development and applications of Ontologies] tutorial
www.sematicweb.org www.ontologyworks.com
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