Web Ontology language: OWL check for unintended relationships between classes automatically classify instances in classes Automated reasoning support allows one to check many more cases than what can be done manually. Checks like the above are valuable for integrating and sharing ontologies from various source Formal semantics and reasoning support is usually provided by mapping an ontology language to a known logical formalism, and by using automated reasoners that already exist for those formalisms. We will see that OWL is (partially) mapped on a description logic, and makes use of existing reasoners such as FaCT and RACER Description logics are a subset of predicate logic for which efficient reason ing support is possible. See 13 for more detail. Limitations of the expressive power of RDF Schema RDF and RDFS allow the representation of some ontological knowledge. The main modelling primitives of RDF/RDFS concern the organization of vocab- ularies in typed hierarchies: subclass and subproperty relationships, domain and range restrictions, and instances of classes. However a number of other features are missing. Here we list a few: say eats, for all classes. Thus in RDF Schema we cannot declare perty, Local scope of properties: rdfs: range defines the range of a pre restrictions that apply to some classes only. For example, we cannot say that cows eat only plants, while other animals may eat meat, too. Disjointness of classes: Sometimes we wish to say that classes are disjoint For example, male and female are disjoint. But in RDF Schema we can only state subclass relationships, e. g. female is a subclass of person Boolean combinations of classes: Sometimes we wish to build new classes by combining other classes using union, intersection and complement. For example, we may wish to define the class person to be the disjoint union of the classes male and female RdF Schema does not allow such definitions Cardinality restrictions: Sometimes we wish to place restrictions on how many distinct values a property may or must take. For example, we woul like to say that a person has exactly two parents, and that a course taught by at least one lecturer. Again such restrictions are impossible to express in RDF Schema. Special characteristics of properties: Sometimes it is useful to say that a property is transitive(like "greater than), unique(like"is mother of") or the inverse of another property(ike“eats”and" is eaten by”)Web Ontology Language: OWL 3 • check for unintended relationships between classes. • automatically classify instances in classes Automated reasoning support allows one to check many more cases than what can be done manually. Checks like the above are valuable for • designing large ontologies, where multiple authors are involved; • integrating and sharing ontologies from various sources. Formal semantics and reasoning support is usually provided by mapping an ontology language to a known logical formalism, and by using automated reasoners that already exist for those formalisms. We will see that OWL is (partially) mapped on a description logic, and makes use of existing reasoners such as FaCT and RACER. Description logics are a subset of predicate logic for which efficient reason￾ing support is possible. See [13] for more detail. Limitations of the expressive power of RDF Schema RDF and RDFS allow the representation of some ontological knowledge. The main modelling primitives of RDF/RDFS concern the organization of vocab￾ularies in typed hierarchies: subclass and subproperty relationships, domain and range restrictions, and instances of classes. However a number of other features are missing. Here we list a few: • Local scope of properties: rdfs:range defines the range of a property, say eats, for all classes. Thus in RDF Schema we cannot declare range restrictions that apply to some classes only. For example, we cannot say that cows eat only plants, while other animals may eat meat, too. • Disjointness of classes: Sometimes we wish to say that classes are disjoint. For example, male and female are disjoint. But in RDF Schema we can only state subclass relationships, e.g. female is a subclass of person. • Boolean combinations of classes: Sometimes we wish to build new classes by combining other classes using union, intersection and complement. For example, we may wish to define the class person to be the disjoint union of the classes male and female. RDF Schema does not allow such definitions. • Cardinality restrictions: Sometimes we wish to place restrictions on how many distinct values a property may or must take. For example, we would like to say that a person has exactly two parents, and that a course is taught by at least one lecturer. Again such restrictions are impossible to express in RDF Schema. • Special characteristics of properties: Sometimes it is useful to say that a property is transitive (like “greater than”), unique (like “is mother of”), or the inverse of another property (like “eats” and “is eaten by”)