Semantic Web Ontologies
Sameer Totey
10/2/2015
CSCI 7818 - Web Infrastructure,
Services, and Applications
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What is Ontology
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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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CSCI 7818 - Web Infrastructure,
Services, and Applications
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What is Ontology for
Web ?
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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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Why Ontologies?
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Lack of a shared understanding
leads to poor communication
Disparate modeling paradigms,
languages and software tools limit
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Interoperability
Knowledge Sharing and reuse
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Theory
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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 nontaxonomically, 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
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The task of developing an
ontology is a typical knowledge
acquisition task involving
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Kickoff
Refinement
Evaluation
Maintenance
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Languages
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There are several representation languages in the AI
(machine learning, natural language processing, knowledge
representation etc) community based on FOL like
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Frame Logic
Loom
Ontololingua etc.
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Web needs XML based language : defining a
language on top of XML syntax
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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)
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DAML (DARPA Agent markup language)
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CSCI 7818 - Web Infrastructure,
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Editors
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Tools that help create ontologies
and metadata that can be used
by multiple agents:
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Protégé
WebOnto
OilEd
ONTOEdit
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Related issues:
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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
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Bremer Semantic Translation project
SKC (Stanford Scalable Knowledge
Composition) project
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References
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http://www.fzi.de/wim
[Development and applications
of Ontologies] tutorial
www.sematicweb.org
www.ontologyworks.com
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10/2/2015
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