Presented by: Mahan Hajianpour

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Ontology Languages for the Semantic Web

• Presented by Mahan Hajianpour

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About the paper

• Name
• Ontology Languages for the Semantic Web
• Year
• 2002
• Authors
• Asunción Gómez-Pérez
• Oscar Corcho
• Universidad Politécnica de Madrid
• Topic
• The authors analyze the most representative
  ontology languages for the web and compare them
  using a common framework

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Presentation Outline

• Goal
• Introduction
• Overview of Ontology Languages
• Comparison Criteria
• Results of Comparison
• Case Study
• Conclusion

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Goal

• The goal of this paper is to help the reader
  understand the difference between the main
  contenders in the realm of ontology languages and
  to aid them in choosing the right language for
  their needs

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IntroductionOverview of Ontologies

• Ontologies are used in
• Agent system
• Knowledge management systems
• e-commerce platforms
• Provide semantic-based access to the Internet
• Semantic Web the conceptual structuring of the
  web in an explicit, machine-readable way
• Ontology An explicit, machine-readable
  specification of a shared conceptualization
• Provide an easy way for machines to gather
  information and build knowledge-based systems
  from applications and/or web sites.

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Overview of Ontology Languages

• XML-based Languages
• Ontology Exchange Language (XOL)
• Simple HTML Ontology Extension (SHOE)
• Ontology Markup Language (OML)
• World Wide Web Consortium (W3C) Languages
• Resource Description Framework (RDF)
• RDF Schema
• Union of RDF and RDF Schema (RDF(S))
• Ontology Inference Layer (OIL)
• DARPA Agent Markup Language (DAMLOIL)

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XML-based Ontology Exchange Language

• Designed by US Bioinformatics community
• Developed for the exchange of ontology
  definitions among a heterogeneous set of software
  systems in their domain
• Based on Ontolingua and OML
• Ontolingua provides high expressiveness of
  knowledge (OKBC) and OML provides syntax based on
  XML
• There are no tools available for development of
  ontologies using XOL
• Any XML editor would be a good tool for this
  purpose

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Simple HTML Ontology Extension

• Developed at the University of Maryland
• Used to develop OML
• Created as an extension of HTML
• Incorporates machine-readable semantic knowledge
  in HTML and other Web documents
• SHOE syntax has been adapted to XML
• Improves search and knowledge gathering
  mechanisms in three phases
• Define an ontology
• Annote HTML pages
• Agent semantically retrieves information

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Ontology Markup Language

• Developed at the University of Washington
• Partially based on SHOE
• Four different levels of OML
• OML Core Logical aspects of the language
• Simple OML Maps directly to RDF(S)
• Abbreviated OML Conceptual graphs features
• Standard OML Most expressive version of OML
• There are no tools for authoring OML other than
  the existing general-purpose XML editors

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Resource Description Framework and RDF Schema

• Developed by W3C
• Developed for describing Web resources
• Allows the specification of the semantics of data
  based on XML in a standardized, interoperable
  manner
• RDF consists of three object types
• Resources Always named by URIs plus optional
  anchor IDs
• Properties Define specific aspects,
  characteristics, attributes, or relations used to
  describe a relation
• Statements Assign a value for a property in a
  specific resource
• RDFS defines the relationship between properties
  and resources (RDF does not)
• RDF(S) is the marriage between RDF and RDFS
• Protégé and Mozilla use RDF(S)

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Ontology Interchange Language

• Developed in the OntoKnowledge project
  (www.ontoknwledge.org/OIL)
• Permits semantic interoperability between web
  resources
• Syntax and semantics based on existing proposals
  (OKBC, XOL and RDF(S))
• OIL built on top of RDF(S) has the following
  layers
• Core OIL groups the OIL primitives that have
  direct mapping to RDF(S) primitives
• Standard OIL is the complete OIL model using more
  primitives than the ones defined in RDF(S)
• Instance OIL adds instances of concepts and roles
  to the previous model
• Heavy OIL is the layer for future extensions of
  OIL
• Tools include OILEd, Protégé2000 and WebODE
• OIL syntax can be expressed in ASCII as well

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DARPA Agent Markup Language OIL

• Developed by the joint committee from the US and
  the European Union (IST)
• DAML is a DARPA project for allowing semantic
  interoperability in XML
• DAMLOIL replaces the initial specification,
  DAML-ONT
• Built on top of RDF(S)
• Tight relationship with OIL
• Tools for authoring DAMLOIL include OILEd,
  OntoEdit, Protégé2000, and WebODE

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Comparison Criteria

• Concepts Anything about which something is said
• Taxonomies Used to organize knowledge using
  generalization and specialization relationships
  through which simple and multiple inheritance
  could be applied
• Relations and Functions The interaction between
  concepts of a domain and attributes
• Axioms Model sentences that are true
• Instances Represent elements in the domain
  attached to a specific concept

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Concepts Overview

• Abstract or complete, elementary or composite,
  real or fictitious
• Also known as classes/objects/categories
• Attributes
• Instance Value different for each instance
• Class Value same for each instance attached to
  concept
• Local Same name attributes attached to different
  concepts
• Global Attributes in which domain is not
  specified
• Predefined Facets
• Default Slot Value Default value for an
  attribute
• Type Constrain the type (also called range)
• Cardinality Constraints Sets min and max number
  of values
• Slot Documentation Definition for the attribute

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Concepts II Questions

• Is it possible to define partitions (sets of
  disjoint concepts) ? For example, table and chair
  can form a partition in a furniture ontology
• Is it possible to define the documentation of the
  concept ?
• Does the language provide mechanisms to define
  the concept attributes ?
• Does the language provide the predefined facets
  for attributes of a class ?

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Taxonomies

• Analyze whether the following primitives are
  predefined in the language
• Subclass of Specializes general concepts into
  more specific concepts
• Disjoint Decomposition A partition where all its
  concepts are subclasses of a common concept
• Exhaustive Subclass Decomposition A complete
  disjoint decomposition
• Not Subclass of Might be used to indicate that a
  subclass is not a specialization of another
  concept

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Relations and Functions I Overview

• Relations are an interaction between concepts of
  the domain and attributes
• Functions are a special kind of relations where
  the value of the last argument is unique for a
  list of values of the n-1 preceding arguments

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Relations and Functions II Questions

• Is it possible to define arbitrary n-ary
  relations or functions ?
• Might the type of the arguments be constrained ?
• Is it possible to define any kind of integrity
  constraints to check the correctness of arguments
  ?
• Is it possible to define operational definitions
  to infer values of arguments with procedure,
  formulas or rules ?

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Axioms

• Used for constraining information, verifying
  correctness, or deducing new information
• Also known as Assertions (e.g. OML)
• Questions
• Is it possible axioms in first order logic,
  second order logic ? ( I order pgtp, II order
  g(p) gt h(p) for all f(p))
• Can we build axioms as independent elements in
  ontology ? (Independent Axioms)
• Can we embed axioms inside the definition of
  other elements ?

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Instances

• Information in distributed resources on semantic
  web is described using instances of concepts and
  relations
• Questions
• Is it possible to define instances of concepts ?
  (e.g. Peter is an instance of class buyer).
• Is it possible to define instances of relations ?
• Does the language provide special mechanisms to
  define claims ? (e.g. John says that Peter has
  brought computer2)

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Results I
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Results II
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Results III
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Types of Ontologies

• Two type of ontologies
• Lightweight Ontologies- Everything except axioms
• Heavyweight Ontologies- Everything including
  axioms
• From lightweight to heavyweight the languaes re
• XOL
• RDF(S)
• SHOE
• OML
• OIL
• DAMLOIL

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Conclusion

• The ontology language used in an application
  should be selected based on the applications
  representational needs
• The semantic web relies on ontology languages to
  function it relies on semantic information
• DAMLOIL offers developers most, if not all, the
  features available in the other languages

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Case Study
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References

• I. Horrocks and F. van Harmelen, Reference
  Description of the DAMLOIL Ontology Markup
  Language, draft report, 2001, www.daml.org/2000/12
  /reference.html (current Jan. 2002).
• D. Brickley and R.V. Guha, Resource Description
  Framework (RDF) Schema Specification, W3C
  Proposed Recommendation, Mar. 1999,
  www.w3.org/TR/PR-rdf-schema (current Jan. 2002).
• R. Studer, R. Benjamins, and D. Fensel,
  Knowledge Engineering Principles and Methods,
  IEEE Trans. on Data and Knowledge Eng., vol. 25,
  nos. 12, 1998, pp. 161197.

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Thank you!