1. Chapter 15

2. 15 Describing Individuals OWL Individuals ▫Ontological Primitive Layer  Mostly described with RDF ▫Instances of user-defined ontological classes ▫Abox (values), not Tbox (schema)

3. 15.1 Determining an Individual Sometimes it is difficult to determine if a given resource is an ▫Individual ▫Instance, or ▫Class A file with individuals: “an instance file” = Abox Individuals: an instance of a concept

4. 15.1.1 Individual vs. Instance Subtle difference - individual and instance ▫Instance is broader term  Anything can have an instance  All individuals are instances, but not vice-versa  A user defined class is an instance of owl:Class ▫Individuals are  Concrete instantiations rather than just concepts  Similar to records in an RDBMS  Similar to objects in object-oriented systems  “That pie over there” versus “key lime pie”

5. 15.1.2 Class vs. Individual Can be tricky to decide if a particular concept is ▫“subclass of” another concept (class) or ▫“instance of” another concept (individual) Answer can vary between different applications ▫OWL Full can consider an individual to be a class ▫Sometimes individual is “prototype” for class Guidelines ▫Individuals should represent actual or virtual objects in the domain of interest ▫Groups of objects should be class concept sets ▫If information is treated as data, define it as an individual ▫If information is used to understand semantics of other data, define it as a class

6. 15.1.3 Leaves of a Taxonomy Concepts are organized into taxonomies (trees) ▫Most specific concepts (leaves) are possible candidates to be individuals  Another test: if values different but properties same Identify lowest level of granularity Consider ▫If A “is a type of” B, then A is a subclass of B ▫If A “is an instance of” B, then A is an individual of class B

7. 15.2 Encoding an Instance File When possible, separate individuals (Abox) from ontologies (Tbox) by storing in different files ▫File with individuals: “instance file”/“artifact file” ▫Ontology files modified infrequently (schema) ▫Instance files modified frequently (records) RDF sufficient for representing most statements about individuals ▫Minimize use of OWL in instance files Software treats Abox and Tbox the same ▫Instance files have same format as ontology files (header, body, footer)

8. 15.3 Instantiating Individuals Use markup tools when possible! ▫Easier and ▫Verifies statement compliance with ontology Instances ▫Created using rdf:ID attribute ▫Associated with a class using  rdf:type attribute and/or  typedNode syntax

9. 15.3.1 Naming Individuals Individuals referenced using URIrefs ▫Assigned using rdf:ID attribute ▫Referenced w/ rdf:about or rdf:resource attributes Individuals can sometimes be “anonymous” ▫No explicit rdf:ID specified No “unique names assumption” ▫Same object may be referenced by >1 URIref Best practice ▫Reuse existing “keys” in rdf:ID  E.g. use employee number as part of rdf:ID identifier to identify a particular employee

10. 15.3.2 Joining a Class An individual asserts membership in a class with ▫rdf:type attribute and/or ▫typedNode syntax Individuals can be members of multiple classes

11. 15.3.2.1 Instantiating Using RDF Descriptions rdf:Description (8.3.4.1) creates an individual ▫rdf:ID “names” individual with URIref  Not required ▫rdf:type attribute assigns individual to class Syntax ▫

12. 15.3.2.2 Instantiating Using Class Name Class typedNode syntax (8.3.6.1.5) creates an individual ▫Can only specify one class this way ▫Can specify additional classes using rdf:type Syntax ▫ Example ▫ ▫“The Knight Owl is a restaurant and a small business”

13. 15.4 Describing an Individual Individuals can be described ▫Where “created” using rdf:ID ▫Later using rdf:about Properties for individuals are defined the same way as making statements about resources (8.3.3)

14. 15.4.1 Associating Property Values at Instantiation Properties can be assigned when instance is created using rdf:ID Syntax ▫ instanceReferences Example ▫ Diner 407-555-1212

15. 15.4.2 Describing Existing Individuals Properties can be assigned for an existing individual after creation using rdf:about Syntax ▫ instanceReferences Example ▫ Diner 407-555-1212

16. 15.4.3 Automating Descriptions of Individuals Since individuals represent “data”, instance files tend to be much larger than ontology files ▫RDF/XML text format not going to replace databases anytime soon ▫Instead, instance files are “views” or “snapshots” Most applications will automatically generate ontology-compliant instance files ▫batch mode or “on-the-fly” as needed

17. 15.5 Relating Individuals OWL provides properties to relate individuals to each other ▫Equivalent individuals  owl:sameAs ▫Different individuals  owl:differentFrom ▫Different groups of individuals  owl:AllDifferent with owl:distinctMembers

18. 15.5.1 Equivalent Individuals owl:sameAs property ▫Specifies that two URIrefs refer to same individual ▫Merges information from different applications ▫Extremely powerful!  Allows “semantic joins” of data across disparate, often unrelated data sources…no database required! ▫Domain & Range: Instance of owl:Thing Syntax ▫ Example ▫

19. 15.5.2 Differentiating Individuals OWL does not follow unique names assumption ▫Every object might be the same as every other! owl:DifferentFrom property ▫Opposite of owl:sameAs ▫Defines pairwise disjointness of two individuals  Better way to handle lots of individuals coming up ▫Domain & Range: Instance of owl:Thing Syntax ▫ Example ▫

20. 15.5.3 Differentiating Groups of Individuals owl:AllDifferent class ▫Asserts that all contained individuals are unique ▫Uses owl:distinctMembers property to enumerate list of disjoint individuals Syntax ▫ members Example ▫

21. 15.6 Describing Individuals Summary Individuals ▫Described using RDF/XML  Should be compliant with an OWL ontology ▫May have multiple URIrefs ▫Members of user-defined classes ▫Described at instantiation or any time later ▫Can be related by equivalence or disjointness Groups of individuals can be declared disjoint

22. Chapter 16

23. 16 OWL Lite Summary OWL ontologies ▫Specified in datafiles using RDF/XML  Header specifies namespaces, versioning, imports ▫Describe classes, properties, and relationships OWL classes ▫Defined with owl:Class  owl:Thing (root class) & owl:Nothing (empty class) OWL properties ▫Relate objects to datatypes, objects, annotations ▫Relate ontologies to each other

24. 16 OWL Lite Summary cont’d OWL property attributes ▫Global restrictions (e.g. Functional) ▫Global inter-property relationships (e.g. inverseOf) ▫Inference shortcuts (eg. Transitive) ▫Local restrictions on classes(values, cardinality) OWL classes also created via derivation ▫Subclasses, equivalency, intersections of classes Individuals ▫Instances of user-defined classes ▫Described at instantiation or later ▫Can be declared equivalent or different

25. 16.1 OWL Lite Constructs GroupConstruct Class/Property Equivalency owl:equivalentClass owl:equivalentProperty Individual Equivalency owl:sameAs owl:differentFrom owl:AllDifferent/ owl:distinctMembers Property Characteristics owl:inverseOf owl:TransitiveProperty owl:SymmetricProperty owl:FunctionalProperty owl:inverseFunctionalProperty GroupConstruct Property Type Restrictions owl:allValuesFrom owl:someValuesFrom owl:intersectionOf Cardinality Restrictions owl:minCardinality (0 or 1) owl:maxCardinality (0 or 1) owl:cardinality (0 or 1) Derived Classes rdfs:subClassOf owl:equivalentClass Header Ontology Information owl:imports owl:priorVersion owl:backwardCompatibleWith owl:incompatibleWith

26. 16.2 OWL Lite Restrictions OWL Lite ▫Subset of OWL Full ▫Goal  Lessen tool requirements  Provide basic functionality  Maintain simplicity  Maintain decidability Restrictions ▫Values, resources, constructs only belong to 1 OWL concept  All classes must be typed as OWL classes  All properties must be typed as OWL properties (object, datatype, annotation, or ontology) ▫Starred items in diagram cannot be mixed (must be disjoint)

27. 16.2 OWL Lite Restrictions cont’d CategoryOWL Full ConstructRestriction Local Property Restrictions owl:allValuesFrom Objects must be named classes or named datatypes owl:someValuesFrom Objects must be named classes or named datatypes Global Property Restrictions rdfs:domain Objects must be named classes rdfs:range Objects must be named classes owl:inverse FunctionalProperty Cannot be defined for datatype properties