Learning ontologies

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Short definition of an ontology

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Learning ontologies

  1. 1. Learning Ontologies By Alexander De Leon Feb 9, 2009
  2. 2. What is an Ontology? “An ontology is a specification of a conceptualization” Person Fe le m Ma al e Father Mother John Maria isMarriedTo Subject Domain Conceptualization Specification(part of the world) (Concepts, Objects, Relationships) Ontology
  3. 3. What is an Ontology?Ontologies are also Computational Artifacts (likeprograms) ∑ ⊨ ...Ontology Inferences or Machine Entailments (Reasoner) INPUT OUTPUT
  4. 4. What can we do with Ontologies?Ontologies allow us to represent domain knowledge,so that we can: Share common understanding. Enable reuse. Make domain assumptions explicit. Separate domain knowledge from operational knowledge.
  5. 5. What can we do with Ontologies?In information systems, manage of information is separatedfrom the application code.A set of services are require for the application to access theinformation (e.g. querying)Ontologies offer a different set of information services thanthose found on XML and RDBMS. Information Application Services component logic
  6. 6. Reasoning Services in OWL-DLConsistency checkingSubsumptionSatisfiabilityEntailmentInstance checkingQuery AnsweringOthers: explanations, approximations, etc.
  7. 7. Semantics vs. Syntax XML Schema (syntactic constraints): <xs:element name= "ParentOfThree" > ... <xs:element ref= "Child" minOccurs= "3" maxOccurs= "3" /> .... </xs:element>Valid XML Document: Invalid XML Document:<ParentOfThree name= "Aphrodite" > <ParentOfThree name= "Aphrodite" > <Child name= "Eros" /> <Child name= "Eros" /> <Child name= "Phobos" /> </ParentOfThree> <Child name= "Himeros" /></ParentOfThree>
  8. 8. Semantics vs. Syntax Ontology Concept: ParentOfThree ≡ Person ⊓ ( = 3 hasChild)Consistent: Also consistent:<ParentOfThree rdf:about="#Aphrodite"> <ParentOfThree rdf:about="#Aphrodite"> <hasChild rdf:resource="#Eros"/> <hasChild rdf:resource="#Eros"/> <ParentOfThree> <hasChild rdf:resource="#Phobos"/> <hasChild rdf:resource="#Himeros"/> <hasChild rdf:resource="#Cupid"/> <ParentOfThree>“Open World Semantics”Lack of “Unique Name Assumption”
  9. 9. OWLSublanguages of OWL OWL-Full: OWL vocabulary with syntactic freedom of RDF and no computational guarantees. OWL-DL & OWL-Lite: OWL-Lite Correspondence to Description Logics formalisms. OWL-DL OWL-DL : Maximum expressivity while maintaining computational RDFS / OWL-Full completeness and decidability.
  10. 10. OWLSublanguages of OWL OWL-Full: OWL vocabulary with syntactic freedom of RDF and no computational guarantees. OWL-DL & OWL-Lite: Correspondence to Description Logics formalisms. OWL-DL : Maximum expressivity while maintaining computational completeness and decidability.
  11. 11. OWLEntities of an OWL ontology are identified by URIs(e.g. http://dumontierlab.com/students/alex)The basic entities are: Class (a concept, e.g. Person) Individual (an object, e.g. John) Object Property (a relationship between two individuals, e.g. loves(John, Susan) ) Data Property (an association between an individual an a piece of data, e.g. age(Alex, 26) )

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