Chapter4 - Chapter 4 Web Ontology Language OWL Grigoris Antoniou Frank van Harmelen 1 Chapter 4 A Semantic Web Primer Lecture Outline 1 2 3 4 5 2 Basic

Chapter4 - Chapter 4 Web Ontology Language OWL Grigoris...

This preview shows page 1 - 10 out of 114 pages.

Chapter 4 A Semantic Web Primer 1 Chapter 4 Web Ontology Language: OWL Grigoris Antoniou Frank van Harmelen
Image of page 1
Chapter 4 A Semantic Web Primer 2 Lecture Outline 1. Basic Ideas of OWL 2. The OWL Language 3. Examples 4. The OWL Namespace 5. Future Extensions
Image of page 2
Chapter 4 A Semantic Web Primer 3 Requirements for Ontology Languages Ontology languages allow users to write explicit, formal conceptualizations of domain models The main requirements are: a well-defined syntax efficient reasoning support a formal semantics sufficient expressive power convenience of expression
Image of page 3
Chapter 4 A Semantic Web Primer 4 Tradeoff between Expressive Power and Efficient Reasoning Support The richer the language is, the more inefficient the reasoning support becomes Sometimes it crosses the border of noncomputability We need a compromise: A language supported by reasonably efficient reasoners A language that can express large classes of ontologies and knowledge.
Image of page 4
Chapter 4 A Semantic Web Primer 5 Reasoning About Knowledge in Ontology Languages Class membership If x is an instance of a class C, and C is a subclass of D, then we can infer that x is an instance of D Equivalence of classes If class A is equivalent to class B, and class B is equivalent to class C, then A is equivalent to C, too
Image of page 5
Chapter 4 A Semantic Web Primer 6 Reasoning About Knowledge in Ontology Languages (2) Consistency X instance of classes A and B, but A and B are disjoint This is an indication of an error in the ontology Classification Certain property-value pairs are a sufficient condition for membership in a class A; if an individual x satisfies such conditions, we can conclude that x must be an instance of A
Image of page 6
Chapter 4 A Semantic Web Primer 7 Uses for Reasoning Reasoning support is important for checking the consistency of the ontology and the knowledge checking for unintended relationships between classes automatically classifying instances in classes Checks like the preceding ones are valuable for designing large ontologies, where multiple authors are involved integrating and sharing ontologies from various sources
Image of page 7
Chapter 4 A Semantic Web Primer 8 Reasoning Support for OWL Semantics is a prerequisite for reasoning support Formal semantics and reasoning support are usually provided by mapping an ontology language to a known logical formalism using automated reasoners that already exist for those formalisms OWL is (partially) mapped on a description logic, and makes use of reasoners such as FaCT and RACER Description logics are a subset of predicate logic for which efficient reasoning support is possible
Image of page 8
Chapter 4 A Semantic Web Primer 9 Limitations of the Expressive Power of RDF Schema Local scope of properties rdfs:range defines the range of a property (e.g.
Image of page 9
Image of page 10

You've reached the end of your free preview.

Want to read all 114 pages?

  • Fall '16
  • gerg dgss
  • OWL, Web Ontology Language, Semantic Web Primer

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture