Controlled vocabularies of the Semantic Web define the concepts and relationships (terms) used to describe a field of interest or area of concern. For instance, to declare a person in a machine-readable format, a vocabulary is needed that has the formal definition of "Person", such as the Friend of a Friend (FOAF) vocabulary, which has a Person class that defines typical properties of a person including, but not limited to, name, honorific prefix, affiliation, email address, and homepage, or the Person vocabulary of Schema.org. Similarly, a book can be described using the Book vocabulary of Schema.org and general publication terms from the Dublin Core vocabulary, an event with the Event vocabulary of Schema.org, and so on.