RDF Triple Stores In the RDF, the subject of a triple represents a real-world object, the triple’s verb represents a property, and the triple’s object represents the value of the property for the subject. This value can be a real-world object or a data value such as a number, a text string, or an image. Real-world objects and properties that are triple subjects, verbs, and objects are identified by Internationalized Resource Identifiers (IRI).15 An IRI can be a Uniform Resource Identifier (URI) that gives the location of a web page, so that the value representing the object or property points to a web page that describes it.16 The RDF Schema (RDFS)17 standard defines the meaning of object class and property for the RDF. Fundamentally, this is not very different to what is meant in ISO/IEC 11179. The Web Ontology Language (OWL)18 is a standard language, based on RDF, for defining ontologies. An ontology describes object classes and properties, and relationships between them. An OWL ontology can be a powerful collection of metadata. RDF, RDFS, and OWL can be used to define standard vocabularies, including the examples given in Table 12. Table 12: Example Standard Vocabularies