foaf

FOAF, short for Friend of a Friend, is a machine-readable vocabulary designed to describe people, their activities, and their social networks on the Web. Built to facilitate interoperability between applications, FOAF represents personal data using RDF, allowing information about people to be shared and linked across services.

The core FOAF vocabulary defines classes such as foaf:Person, foaf:Organization, and foaf:Agent (with foaf:Person being a subclass of foaf:Agent). It provides properties to capture name information (foaf:name, foaf:givenName, foaf:familyName), contact details (foaf:mbox, foaf:phone), online identity (foaf:homepage, foaf:account), and social connections (foaf:knows). Other terms include foaf:depiction for images and foaf:PersonalProfileDocument for representing a user profile as RDF. FOAF profiles are typically serialized in RDF formats such as RDF/XML or Turtle, using the foaf: namespace at http://xmlns.com/foaf/0.1/.

FOAF was developed in the early 2000s by contributors including Libby Miller and Dan Brickley. The project aimed to provide a standard way to publish personal data and social graphs on the Semantic Web, enabling data fusion and reuse across different systems. While FOAF played a influential role in early linked data and social data publishing, its adoption has varied, with some projects using FOAF alongside or in place of other personal data vocabularies. Today, FOAF remains a reference vocabulary for describing people and their networks in RDF, illustrating the principles of interoperability and machine-readable social information. Privacy considerations and platform-specific restrictions continue to affect how FOAF data is shared and utilized.