FOAF logo.

FOAF (an acronym of Friend of a friend) is a machine-readable ontology describing persons, their activities and their relations to other people and objects. Anyone can use FOAF to describe him or herself. FOAF allows groups of people to describe social networks without the need for a centralised database.

FOAF is a descriptive vocabulary expressed using the Resource Description Framework (RDF) and the Web Ontology Language (OWL). Computers may use these FOAF profiles to find, for example, all people living in Europe, or to list all people both you and a friend of yours know^[1][2]. This is accomplished by defining relationships between people. Each profile has a unique identifier (such as the person's e-mail addresses, a Jabber ID, or a URI of the homepage or weblog of the person), which is used when defining these relationships.

The FOAF project, which defines and extends the vocabulary of a FOAF profile, was started in 2000 by Libby Miller and Dan Brickley. It can be considered the first Social Semantic Web application, in that it combines RDF technology with 'Social Web' concerns.

Tim Berners-Lee in a 2007 essay ^[3] redefined the Semantic web concept into something he calls the Giant Global Graph, where relationships transcend networks/documents. He considers the GGG to be on equal grounds with Internet and World Wide Web, stating that "I express my network in a FOAF file, and that is a start of the revolution."

[edit] FOAF+SSL

FOAF+SSL^[4] is the decentralized secure authentication protocol utilizing the FOAF profile information as well as the SSL security layer usually available in virtually all modern web browsers. It was first presented^[5] for the W3C Workshop on the Future of Social Networking in 2009. Contrary to the usual SSL utilization patterns, it does not require^[6] the dedicated key signing parties such as Certificate authority to perform the user authorization.

[edit] Deployment

Being an early example of a Semantic Web application, and having a relatively simple use-case and standard has led FOAF to be adopted widely on the web. For example, the Live Journal and DeadJournal blogging sites exports FOAF profiles for all their members^[7], My Opera community exports FOAF profiles for the members as well as for the groups, the FOAF support is known to be present on Identi.ca, MyBlogLog, FriendFeed, TypePad services, as well as on various other ones^[8]. Yandex blog search platform supports^[9] search over the FOAF profile information. The prominent client-side FOAF support is available in Safari^[10] web browser, as well as in the Semantic Radar^[11] plugin for Firefoxbrowser.

There are also modules or plugins to support FOAF profiles or FOAF+SSL authorization for programming languages^[12][13], as well as for content management systems^[14].

[edit] Example

The following FOAF profile (written in Turtle format) states that Jimmy Wales is the name of the person described here. His e-mail address, homepage and depiction are resources, which means that each of them can be described using RDF as well. He has Wikimedia as an interest, and knows Angela Beesley (which is the name of a 'Person' resource).

 @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .   <#JW>     a foaf:Person ;     foaf:name "Jimmy Wales" ;     foaf:mbox <mailto:jwales@bomis.com> ;     foaf:homepage <http://www.jimmywales.com/> ;     foaf:nick "Jimbo" ;     foaf:depiction <http://www.jimmywales.com/aus_img_small.jpg> ;     foaf:interest <http://www.wikimedia.org> ;     foaf:knows [         a foaf:Person ;         foaf:name "Angela Beesley"     ] .   <http://www.wikimedia.org>     rdfs:label "Wikipedia" . 

[edit] See also

• Resource Description Framework (RDF)
• Web Ontology Language (OWL)
• Social web
• Semantic Web
• Description of a Career (DOAC)
• Description of a Project (DOAP)
• Semantically-Interlinked Online Communities (SIOC)
• hCard (HTML vCard)
• XHTML Friends Network (XFN)

[edit] References

1. ^ XML Watch: Finding friends with XML and RDF by Edd Dumbill in IBM DeveloperWorks
2. ^ XML Watch: Support online communities with FOAF by Edd Dumbill in IBM DeveloperWorks
3. ^ Giant Global Graph, Tim Berners Lee
4. ^ FOAF+SSL decentralized authentication protocol.
5. ^ foaf+ssl: adding security to open distributed social networks - for the "W3C Workshop on the Future of Social Networking", which took place in Barcelona January 2009
6. ^ http://blogs.sun.com/bblfish/entry/more_on_authorization_in_foaf - foaf+ssl: creating a web of trust without key signing parties
7. ^ Details on LiveJournal FOAF, http://community.livejournal.com/ljfoaf
8. ^ Known FOAF data providers.
9. ^ Yandex press release on the social networking support.
10. ^ FOAF Support in Safari RSS
11. ^ Semantic Radar plugin for Firefox browser
12. ^ http://search.cpan.org/~btrott/XML-FOAF-0.03/lib/XML/FOAF.pm - FOAF support module for Perl
13. ^ http://search.cpan.org/~tobyink/CGI-Auth-FOAF_SSL-0.52/lib/CGI/Auth/FOAF_SSL.pm - FOAF+SSL authentication support for Perl
14. ^ http://drupal.org/project/foaf - FOAF support for Drupal

[edit] External links

• The FOAF Project
• FOAF dataset a dataset of 201,612 FOAF triples

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