1. OWL TUTORIAL APT CSA 3003 OWL ANNOTATOR Charlie Abela CSAI Department

2. OWL TUTORIAL 2 Charlie Abela Outline Ontologies Web Ontology Language: OWL Flavours of OWL Some Differences Classes Properties Individuals Namespaces and Headers

3. OWL TUTORIAL 3 Charlie Abela Ontologies Ontologies were developed in Artificial Intelligence to facilitate knowledge sharing and reuse. Ontologies provide a machine-processable semantics of information sources that can be communicated between different agents An ontology is a formal, explicit specification of a shared conceptualisation [Gruber, 1993]  A ‘conceptualisation’ refers to an abstract model of some phenomenon in the world which identifies the relevant concepts of that phenomenon.  ‘Explicit’ means that the type of concepts used and the constraints on their use are explicitly defined.  ‘Formal’ refers to the fact that the ontology should be machine readable.

4. OWL TUTORIAL 4 Charlie Abela OWL Web Ontology Language is a language for defining and instantiating Web ontologies OWL is intended to provide a language that can be used to describe the classes and relations (properties) between them that are inherent in Web documents and applications. OWL has more facilities for expressing meaning and semantics than XML, RDF, and RDF-S  Reasoning capabilities provided by tools

5. OWL TUTORIAL 5 Charlie Abela Flavours of OWL OWL Lite supports those users primarily needing a classification hierarchy and simple constraint features OWL DL supports those users who want the maximum expressiveness without losing computational completeness and decidability of reasoning systems OWL Full is meant for users who want maximum expressiveness and the syntactic freedom of RDF with no computational guarantees

6. OWL TUTORIAL 6 Charlie Abela Some Differences OWL Lite supports cardinality constraints, but it only permits cardinality values of 0 or 1 In OWL Lite and OWL DL an individual can never be at the same time a class: classes and individuals form disjoint domains In OWL Lite there is no support for boolean constructors, unionOf (OR) and complementOf (not). Some limited support for intersectionOf (AND) In OWL Lite there is no support for one of (EnumeratedClass) constructor.

7. OWL TUTORIAL 7 Charlie Abela Class Descriptions A class identifier (a URI reference) A property restriction : value Universal Quantifier (Class of all individuals whose Parents are Human) <owl:allValuesFrom rdf:resource="#Human"/ Existential Quantifier (Class of individuals who have at least one parent a Physician)

8. OWL TUTORIAL 8 Charlie Abela Class Descriptions (2) A property restriction: cardinality <owl:maxCardinality rdf:datatype="&xsd;nonNegativeInteger">2 Other constructs: minCardinality and cardinality The intersectionOf two or more class descriptions

9. OWL TUTORIAL 9 Charlie Abela Class Axioms Class descriptions form the building blocks for defining classes through class axioms:  rdfs:subClassOf  owl:equivalentClass <owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger">1

10. OWL TUTORIAL 10 Charlie Abela Properties OWL distinguishes between two types of properties:  Object properties: have a value range of class individuals, and thus link individuals to individuals.  Datatype properties have a value range of data values, and thus link individuals to data values.

11. OWL TUTORIAL 11 Charlie Abela Properties (2)

12. OWL TUTORIAL 12 Charlie Abela Property Characteristics inverseOf FunctionalProperty: is a property that can have only one (unique) value y for each instance x. ( a Woman can have only one husband) InverseFunctionalProperty: where a range value uniquely determines the domain value (every human has only one biological mother)

13. OWL TUTORIAL 13 Charlie Abela Logical Property Characteristics owl:TransitiveProperty: P(x,y) and P(y,z) implies P(x,z) owl:SymmetricProperty: P(x,y) iff P(y,x)

14. OWL TUTORIAL 14 Charlie Abela Individuals Individual axioms are statements about individuals, indicating class membership and statements about relevant properties 1900-01- 14 <numberOfActs rdf:datatype="&xsd;positiveInteger">3

15. OWL TUTORIAL 15 Charlie Abela Individual Identity On the web it is not possible to have unique names for different things. OWL provides three constructs for making statements about the identity of individuals:  owl:sameAs is used to state that two URI references refer to the same individual. The construct owl:sameIndividualAs is a synonym of owl:sameAs  owl:differentFrom is used to state that two URI references refer to different individuals  owl:AllDifferent provides an idiom for stating that a list of individuals are all different.

16. OWL TUTORIAL 16 Charlie Abela Individual Identity (2) owl:distinctMembers can only be used in combination with owl:AllDifferent

17. OWL TUTORIAL 17 Charlie Abela Namespaces <rdf:RDF xmlns ="http://www.w3.org/TR/………../wine#" xmlns:vin ="http://www.w3.org/TR/……/wine#" xml:base ="http://www.w3.org/TR/……./wine#" xmlns:food="http://www.w3.org/TR/….../food#" xmlns:owl ="http://www.w3.org/2002/07/owl#" xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:xsd ="http://www.w3.org/2001/XMLSchema#"> Abbreviations can be defined using an ENTITY definition <!DOCTYPE rdf:RDF [ <!ENTITY vin "http://www.w3.org/TR/………/wine#" ]> <rdf:RDF xmlns ="&vin;" xmlns:vin ="&vin;" xml:base ="&vin;" xmlns:food="&food;" …….>

18. OWL TUTORIAL 18 Charlie Abela Headers Example OWL ontology Wine Ontology ……….

19. OWL TUTORIAL 19 Charlie Abela Importing Ontologies owl:imports: references another OWL ontology containing definitions, whose meaning is considered to be part of the meaning of the importing ontology. If an OWL Lite ontology imports an OWL DL or OWL Full ontology, it effectively becomes an OWL DL or OWL Full ontology. If ontology A imports B, and B imports C, then A imports both B and C