I've recently discovered RDF, one of the web's rising frameworks for identifying and describing data, made for the web of linked data. It can describe people, institutions, accounts, places, events, languages, documents, and much more thanks to the vast range of standardized vocabularies for different concepts, entities, and relations. The core unit of information in RDF is the semantic triple: subject, predicate, and object. The individual concepts (resources) are identified with URIs, brining universal identification, verification, and navigation to pieces of data.
There are numerous vocabularies (ontologies) for RDF, and one of them is FOAF (Friend of a Friend), used for describing people and their online presence, as well as general groups of people. One of the properties a group in FOAF (class foaf:Group) can have is foaf:membershipClass. This states that people in a specific group can be thought of as members of a particular class, that the two sets of people are equal.
There is also OWL, an ontology of ontologies, a vocabulary for describing vocabularies. The purpose of this metaontology is assisting reasoners in deriving additional facts from data, forming a complex knowledge base. Even though there are simpler schemata that are sometimes enough (RDFS), OWL defines things like identity, equivalency of classes and properties, and constructions of anonymous classes and properties in terms of relations to other classes and properties.
There are parts of FOAF that are hard to describe using OWL, and foaf:membershipClass is one of those, since it links an individual (group) to a class. I will now try to describe it with OWL (using the Turtle language).
