Chapter 4 Web Ontology Language: OWL Grigoris Antoniou Frank van Harmelen 1 Chapter 4 A Semantic Web Primer
1 Chapter 4 A Semantic Web Primer Chapter 4 Web Ontology Language: OWL Grigoris Antoniou Frank van Harmelen
Lecture Outline Basic Ideas of owl 2. The oWL Language 3. Examples 4. The oWL Namespace 5. Future Extensions Chapter 4 A Semantic Web primer
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
Requirements for Ontology Languages o 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 3 Chapter 4 A Semantic Web primer
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
Tradeoff between Expressive Power and Efficient Reasoning Support o The richer the language is, the more inefficient the reasoning support becomes e 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 Chapter 4 A Semantic Web primer
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
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 5 Chapter 4 A Semantic Web primer
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