be identified by a URI (http://www.example.org/tea.owl, say). This example provides a sense of the syntax. To save space below, preambles and prefix definitions have been skipped. OWL2 Functional Syntax Ontology(<http://example.org/tea.owl> Declaration( Class( :Tea ) ) ) OWL2 XML Syntax <Ontology ontologyIRI="http://example.org/tea.owl" ...> <Prefix name="owl" IRI="http://www.w3.org/2002/07/owl#"/> <Declaration> <Class IRI="Tea"/> </Declaration> </Ontology> Manchester Syntax Ontology: <http://example.org/tea.owl> Class: Tea RDF/XML syntax<rdf:RDF ...> <owl:Ontology rdf:about=""/> <owl:Class rdf:about="#Tea"/> </rdf:RDF> RDF/Turtle <http://example.org/tea.owl> rdf:type owl:Ontology . :Tea rdf:type owl:Class . Semantics Relation to description logics OWL classes correspond to description logic (DL) concepts, OWL properties to DL roles, while individuals are called the same way in both the OWL and the DL terminology. Early attempts to build large ontologies were plagued by a lack of clear definitions. Members of the OWL family have model theoretic formal semantics, and so have strong logical foundations. Description logics are a family of logics that are decidable fragments of first-order logic with attractive and well-understood computational properties. OWL DL and OWL Lite semantics are based on DLs. They combine a syntax for describing and exchanging ontologies, and formal semantics that gives them meaning. For example, OWL DL corresponds to the description logic, while OWL 2 corresponds to the logic. Sound, complete, terminating reasoners (i.e. systems which are guaranteed to derive every consequence of the knowledge in an ontology) exist for these DLs. Relation to RDFS OWL Full is intended to be compatible with RDF Schema (RDFS), and to be capable of augmenting the meanings of existing Resource Description Framework (RDF) vocabulary. A model theory describes the formal semantics for RDF. This interpretation provides the meaning of RDF and RDFS vocabulary. So, the meaning of OWL Full ontologies are defined by extension of the RDFS meaning, and OWL Full is a semantic extension of RDF. Open world assumption The languages in the OWL family use the open world assumption. Under the open world assumption, if a statement cannot be proven to be true with current knowledge, we cannot draw the conclusion that the statement is false. Contrast to other languages A relational database consists of sets of tuples with the same attributes. SQL is a query and management language for relational databases. Prolog is a logical programming language. Both use the closed world assumption. Terminology Languages in the OWL family are capable of creating classes, properties, defining instances and its operations. Instances An instance is an object. It corresponds to a description