4.1. Semantics on the Web4.1.1. Motivating Factors4.1.1.1. Understanding the World Wide Web4.1.1.2. Knowledge Domain Integration4.1.2. Expressing Semantics in RDF4.1.2.1. Vocabularies, Taxonomies, and Ontologies4.1.2.2. A Vocabulary Language for RDF4.1.2.3. An Ontology Language for the Web4.2. Introduction to Ontologies4.2.1. Distributed Knowledge4.2.1.1. Open World Assumption4.2.1.2. No Unique Names Assumption4.2.2. Overview of Ontology Elements4.2.2.1. Ontology Header4.2.2.2. Classes and Individuals4.2.2.3. Properties4.2.2.4. Annotations4.2.2.5. Datatypes4.3. Elements of an Ontology4.3.1. OWL 2 Typing4.3.2. Ontology Header4.3.3. Annotations4.3.4. Basic Classification4.3.4.1. Classes and Individuals4.3.4.2. rdfs:SubClassOf4.3.4.3. Instance versus Subclass4.3.4.4. owl:Thing and owl:Nothing4.3.5. Defining and Using Properties4.3.6. Property Domain and Range4.3.7. Describing Properties4.3.7.1. rdfs:subPropertyOf4.3.7.2. Top and Bottom Properties4.3.7.3. Inverse Properties4.3.7.4. Disjoint Properties4.3.7.5. Property Chains4.3.7.6. Symmetric, Reflexive, and Transitive Properties4.3.7.7. Functional and Inverse Functional Properties4.3.7.8. Keys4.3.8. Datatypes4.3.8.1. Datatype Restrictions4.3.8.2. Defining Datatypes in Terms of Other Datatypes4.3.9. Negative Property Assertions4.3.10. Property Restrictions4.3.10.1. Value Restrictions4.3.10.2. Cardinality Restrictions4.3.10.3. Qualified Cardinality Restrictions4.3.11. Advanced Class Description4.3.11.1. Enumerating Class Membership4.3.11.2. Set Operators4.3.11.3. Disjoint Classes4.3.12. Equivalence in OWL4.3.12.1. Equivalence among Individuals4.3.12.2. Equivalence among Classes and Properties4.4. Summary