FOAF Vocabulary Specification

This work is licensed under a Creative Commons Attribution License. This copyright applies to the FOAF Vocabulary Specification and accompanying documentation in RDF. Regarding underlying technology, FOAF uses W3C's RDF technology, an open Web standard that can be freely used by anyone.

Abstract

This specification describes the FOAF language, defined as a dictionary of named properties and classes using W3C's RDF technology.

FOAF is a project devoted to linking people and information using the Web. Regardless of whether information is in people's heads, in physical or digital documents, or in the form of factual data, it can be linked. FOAF integrates three kinds of network: social networks of human collaboration, friendship and association; representational networks that describe a simplified view of a cartoon universe in factual terms, and information networks that use Web-based linking to share independently published descriptions of this inter-connected world. FOAF does not compete with socially-oriented Web sites; rather it provides an approach in which different sites can tell different parts of the larger story, and by which users can retain some control over their information in a non-proprietary format.

Status of This Document

FOAF has been evolving gradually since its creation in mid-2000. There is now a stable core of classes and properties that will not be changed, beyond modest adjustments to their documentation to track implementation feedback and emerging best practices. New terms may be added at any time (as with a natural-language dictionary), and consequently this specification is an evolving work. The FOAF RDF namespace URI, by contrast, is fixed and its identifier is not expected to change. Furthermore, efforts are underway to ensure the long-term preservation of the FOAF namespace, its xmlns.com domain name and associated documentation.

The FOAF specification is produced as part of the FOAF project, to provide authoritative documentation of the contents, status and purpose of the RDF/XML vocabulary and document formats known informally as 'FOAF'.

This document is created by combining the RDFS/OWL machine-readable FOAF ontology with a set of per-term documents. Future versions may incorporate multilingual translations of the term definitions. An RDF/XML encoding of the specification is available by direct link or by HTTP content negotiation from the namespace URI. The HTML specification no longer embeds the RDF/XML markup; however an experimental subset of the RDF is included in this document using RDFa notation.

The authors welcome comments on this document, preferably via the public FOAF developers list foaf-dev@lists.foaf-project.org; public archives are available. A historical backlog of known technical issues is acknowledged, and available for discussion on the FOAF mailing list. Proposals for resolving these issues are welcomed, on foaf-dev. Further work is also needed on the explanatory text in this specification and on the FOAF website; progress towards this will be measured in the version number of future revisions to the FOAF specification.

Changes in version 0.99

This revision stablises weblog, page, Document and Image and adds three owl:equivalent classes to schema.org - Person (Person), Image (ImageObject), Document (CreativeWork).

See the changes section for more detailed change-log information.

FOAF at a glance

FOAF describes the world using simple ideas inspired by the Web. In FOAF descriptions, there are only various kinds of things and links, which we call properties. The types of the things we talk about in FOAF are called classes. FOAF is therefore defined as a dictionary of terms, each of which is either a class or a property. Other projects alongside FOAF provide other sets of classes and properties, many of which are linked with those defined in FOAF.

FOAF descriptions are themselves published as linked documents in the Web (eg. using RDF/XML or RDFa syntax). The result of the FOAF project is a network of documents describing a network of people (and other stuff). Each FOAF document is itself an encoding of a descriptive network structure. Although these documents do not always agree or tell the truth, they have the useful characteristic that they can be easily merged, allowing partial and decentralised descriptions to be combined in interesting ways.

FOAF collects a variety of terms; some describe people, some groups, some documents. Different kinds of application can use or ignore different parts of FOAF. The overview here shows one way of viewing FOAF terms: we ignore archaic and historical parts, and divide the rest into terms that only make sense on the Web, and those that have universal applicability when linking people and information.

Main FOAF terms, grouped in broad categories.

Core - These classes and properties form the core of FOAF. They describe characteristics of people and social groups that are independent of time and technology; as such they can be used to describe basic information about people in present day, historical, cultural heritage and digital library contexts. In addition to various characteristics of people, FOAF defines classes for Project, Organization and Group as other kinds of agent. Related work: Dublin Core, SKOS, DOAP, SIOC, Org vocabulary, Bio vocabulary.
Social Web - in addition to the FOAF core terms, there are a number of terms for use when describing Internet accounts, addressbooks and other Web-based activities. Related work: Portable Contacts, W3C Social Web group.
Linked Data utilities - FOAF began as the 'RDFWeb' project, and established a widely adopted model for publishing simple factual data via a networked of linked RDF documents. FOAF remains important to the growing "Linked Data" community, while also maintaining a concern for information that is not readily summarised as simple factual data. FOAF is an attempt to use the Web to integrate factual information with information in human-oriented documents (eg. videos, books, spreadsheets, 3d models), as well as information that is still in people's heads. This history explains why FOAF includes a few 'demonstration' terms that served largely educational purposes (eg. geekcode), alongside a few technical utility terms (eg. focus, LabelProperty) that support wider information-linking efforts. The dictionary-based design of FOAF allows a certain pragmatism: we simply record here a set of terms that are useful to the Web community, while keeping an emphasis on the central idea of FOAF, which is about linking networks of information with networks of people.

FOAF Core

- Agent
- Person
- name
- title
- img
- depiction (depicts)
- familyName
- givenName
- knows
- based_near
- age
- made (maker)
- primaryTopic (primaryTopicOf)
- Project
- Organization
- Group
- member
- Document
- Image

A-Z of FOAF terms (current and archaic)

This is a complete alphabetical A-Z index of all FOAF terms, by class (categories or types) and by property. Note that it includes 'archaic' terms that are largely of historical interest.

Example

This brief example introduces the basics of FOAF. It basically says, "there is a foaf:Person with a foaf:name property of 'Dan Brickley'; this person stands in foaf:homepage and foaf:openid relationship to a thing called https://www.downtownmelody.com/_x/ZGFuYnJpLm9yZw/ and a foaf:img relationship to a thing referenced by a relative URI of /images/me.jpg

1 Introduction: FOAF Basics

The Semantic Web

FOAF is a project devoted to linking people and information using the Web. Regardless of whether information is in people's heads, in physical or digital documents, or in the form of factual data, it can be linked. FOAF integrates three kinds of network: social networks of human collaboration, friendship and association; representational networks that describe a simplified view of a cartoon universe in factual terms, and information networks that use Web-based linking to share independently published descriptions of this inter-connected world. FOAF does not compete with socially-oriented Web sites; rather it provides an approach in which different sites can tell different parts of the larger story, and through which users can retain some control over their information in a non-proprietary format.

FOAF and the Semantic Web

FOAF, like the Web itself, is a linked information system. It is built using decentralised Semantic Web technology, and has been designed to allow for integration of data across a variety of applications, Web sites and services, and software systems. To achieve this, FOAF takes a liberal approach to data exchange. It does not require you to say anything at all about yourself or others, nor does it place any limits on the things you can say or the variety of Semantic Web vocabularies you may use in doing so. This current specification provides a basic "dictionary" of terms for talking about people and the things they make and do.

FOAF was designed to be used alongside other such dictionaries ("schemas" or "ontologies"), and to be usable with the wide variety of generic tools and services that have been created for the Semantic Web. For example, the W3C work on SPARQL provides us with a rich query language for consulting databases of FOAF data, while the SKOS initiative explores in more detail than FOAF the problem of describing topics, categories, "folksonomies" and subject hierarchies. Meanwhile, other W3C groups are working on improved mechanisms for encoding all kinds of RDF data (including but not limited to FOAF) within Web pages: see the work of the GRDDL and RDFa efforts for more detail. The Semantic Web provides us with an architecture for collaboration, allowing complex technical challenges to be shared by a loosely-coordinated community of developers.

The FOAF project is based around the use of machine readable Web homepages for people, groups, companies and other kinds of thing. To achieve this we use the "FOAF vocabulary" to provide a collection of basic terms that can be used in these Web pages. At the heart of the FOAF project is a set of definitions designed to serve as a dictionary of terms that can be used to express claims about the world. The initial focus of FOAF has been on the description of people, since people are the things that link together most of the other kinds of things we describe in the Web: they make documents, attend meetings, are depicted in photos, and so on.

The FOAF Vocabulary definitions presented here are written using a computer language (RDF/OWL) that makes it easy for software to process some basic facts about the terms in the FOAF vocabulary, and consequently about the things described in FOAF documents. A FOAF document, unlike a traditional Web page, can be combined with other FOAF documents to create a unified database of information. FOAF is a Linked Data system, in that it based around the idea of linking together a Web of decentralised descriptions.

The Basic Idea

The basic idea is pretty simple. If people publish information in the FOAF document format, machines will be able to make use of that information. If those files contain "see also" references to other such documents in the Web, we will have a machine-friendly version of today's hypertext Web. Computer programs will be able to scutter around a Web of documents designed for machines rather than humans, storing the information they find, keeping a list of "see also" pointers to other documents, checking digital signatures (for the security minded) and building Web pages and question-answering services based on the harvested documents.

So, what is the 'FOAF document format'? FOAF files are just text documents (well, Unicode documents). They adopt the conventions of the Resource Description Framework (RDF), and may be written in XML syntax or any other of the syntaxes of RDF such as RDFa or N3. In addition, the FOAF vocabulary defines some useful constructs that can appear in FOAF files, alongside other RDF vocabularies defined elsewhere. For example, FOAF defines categories ('classes') such as foaf:Person, foaf:Document, foaf:Image, alongside some handy properties of those things, such as foaf:name, foaf:mbox (ie. an internet mailbox), foaf:homepage etc., as well as some useful kinds of relationship that hold between members of these categories. For example, one interesting relationship type is foaf:depiction. This relates something (eg. a foaf:Person) to a foaf:Image. The FOAF demos that feature photos and listings of 'who is in which picture' are based on software tools that parse RDF documents and make use of these properties.

The specific contents of the FOAF vocabulary are detailed in this FOAF namespace document. In addition to the FOAF vocabulary, one of the most interesting features of a FOAF file is that it can contain "see Also" pointers to other FOAF files. This provides a basis for automatic harvesting tools to traverse a Web of interlinked files, and learn about new people, documents, services, data...

The remainder of this specification describes how to publish and interpret descriptions such as these on the Web, using RDF/XML for syntax (file format) and terms from FOAF. It introduces a number of categories (RDF classes such as 'Person') and properties (relationship and attribute types such as 'mbox' or 'workplaceHomepage'). Each term definition is provided in both human and machine-readable form, hyperlinked for quick reference.

What's FOAF for?

The co-depiction experiment shows a fun use of the vocabulary. To create a FOAF document, you can use Leigh Dodd's FOAF-a-matic javascript tool. For more information on FOAF and related projects, see the FOAF project home page.

Background

FOAF is a collaborative effort amongst developers on the FOAF (foaf-dev@lists.foaf-project.org) mailing list. The name 'FOAF' is derived from traditional internet usage, an acronym for 'Friend of a Friend'.

The name was chosen to reflect our concern with social networks and the Web, urban myths, trust and connections. Other uses of the name continue, notably in the documentation and investigation of Urban Legends (eg. see the alt.folklore.urban archive or snopes.com), and other FOAF stories. Our use of the name 'FOAF' for a Web vocabulary and document format is intended to complement, rather than replace, these prior uses. FOAF documents describe the characteristics and relationships amongst friends of friends, and their friends, and the stories they tell.

FOAF and Standards

It is important to understand that the FOAF vocabulary as specified in this document is not a standard in the sense of ISO Standardisation, or that associated with W3C Process.

FOAF depends heavily on W3C's standards work, specifically on XML, XML Namespaces, RDF, and OWL. All FOAF documents must be well-formed RDF documents. The FOAF vocabulary, by contrast, is managed more in the style of an Open Source or Free Software project than as an industry standardarisation effort (eg. see Jabber JEPs).

This specification contributes a vocabulary, "FOAF", to the Semantic Web, specifying it using W3C's Resource Description Framework (RDF). As such, FOAF adopts by reference both syntaxes (using XML, N3, or RDFa) a data model (RDF graphs) and a mathematically grounded definition for the rules that underpin the FOAF design.

The FOAF Vocabulary Description

This specification serves as the FOAF "namespace document". As such it describes the FOAF vocabulary the terms (RDF classes and properties) that constitute it, so that Semantic Web applications can use those terms in a variety of RDF-compatible document formats and applications.

This document presents FOAF as a Semantic Web vocabulary or Ontology. The FOAF vocabulary is pretty simple, pragmatic and designed to allow simultaneous deployment and extension. FOAF is intended for widescale use, but its authors make no commitments regarding its suitability for any particular purpose.

Evolution and Extension of FOAF

The FOAF vocabulary is identified by the namespace URI 'https://www.downtownmelody.com/_x/eG1sbnMuY29t/foaf/0.1/'. Revisions and extensions of FOAF are conducted through edits to this document, which by convention is accessible in the Web via the namespace URI. For practical and deployment reasons, note that we do not update the namespace URI as the vocabulary matures.

Much of FOAF now is considered stable. Each release of this specification document has an incrementally increased version number, even while the technical namespace ID remains fixed and includes the original value of "0.1". It long ago became impractical to update the namespace URI without causing huge disruption to both producers and consumers of FOAF data. We are left with the digits "0.1" in our URI. This stands as a warning to all those who might embed metadata in their vocabulary identifiers.

The evolution of FOAF is best considered in terms of the stability of individual vocabulary terms, rather than the specification as a whole. As terms stabilise in usage and documentation, they progress through the categories 'unstable', 'testing' and 'stable'. Older terms are marked 'archaic' which allows the possibility of older forms to become modern again.

The properties and types defined here provide some basic useful concepts for use in FOAF descriptions. Other vocabulary (eg. the Dublin Core metadata elements for simple bibliographic description), RSS 1.0 etc can also be mixed in with FOAF terms, as can local extensions. FOAF is designed to be extended.

FOAF Auto-Discovery: Publishing and Linking FOAF files

If you publish a FOAF self-description (eg. using foaf-a-matic) you can make it easier for tools to find your FOAF by putting markup in the head of your HTML homepage. It doesn't really matter what filename you choose for your FOAF document, although foaf.rdf is a common choice. The linking markup is as follows:

...although of course change the URL to point to your own FOAF document. See also: more on FOAF autodiscovery and services that make use of it.

FOAF cross-reference: Listing FOAF Classes and Properties

FOAF introduces the following classes and properties. A machine-friendly version is also available in RDF/XML.

Classes and Properties (full detail)

Classes

Class: foaf:Agent

Agent - An agent (eg. person, group, software or physical artifact).

Status:	stable
Properties include:	gender yahooChatID account birthday icqChatID aimChatID jabberID made mbox interest tipjar skypeID topic_interest age mbox_sha1sum status msnChatID openid holdsAccount weblog
Used with:	maker member
Has Subclass	Group Person Organization

The Agent class is the class of agents; things that do stuff. A well known sub-class is Person, representing people. Other kinds of agents include Organization and Group.

The Agent class is useful in a few places in FOAF where Person would have been overly specific. For example, the IM chat ID properties such as jabberID are typically associated with people, but sometimes belong to software bots.

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Class: foaf:Document

Document - A document.

Status:	stable
Properties include:	topic primaryTopic sha1
Used with:	workInfoHomepage workplaceHomepage page accountServiceHomepage openid tipjar schoolHomepage publications isPrimaryTopicOf interest homepage weblog
Has Subclass	Image PersonalProfileDocument

Disjoint With:	Project Organization

The Document class represents those things which are, broadly conceived, 'documents'.

The Image class is a sub-class of Document, since all images are documents.

We do not (currently) distinguish precisely between physical and electronic documents, or between copies of a work and the abstraction those copies embody. The relationship between documents and their byte-stream representation needs clarification (see sha1 for related issues).

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Class: foaf:Group

Group - A class of Agents.

Status:	stable
Properties include:	member
Subclass Of	Agent

The Group class represents a collection of individual agents (and may itself play the role of a Agent, ie. something that can perform actions).

This concept is intentionally quite broad, covering informal and ad-hoc groups, long-lived communities, organizational groups within a workplace, etc. Some such groups may have associated characteristics which could be captured in RDF (perhaps a homepage, name, mailing list etc.).

While a Group has the characteristics of a Agent, it is also associated with a number of other Agents (typically people) who constitute the Group. FOAF provides a mechanism, the membershipClass property, which relates a Group to a sub-class of the class Agent who are members of the group. This is a little complicated, but allows us to make group membership rules explicit.

The markup (shown below) for defining a group is both complex and powerful. It allows group membership rules to match against any RDF-describable characteristics of the potential group members. As FOAF and similar vocabularies become more expressive in their ability to describe individuals, the Group mechanism for categorising them into groups also becomes more powerful.

While the formal description of membership criteria for a Group may be complex, the basic mechanism for saying that someone is in a Group is very simple. We simply use a member property of the Group to indicate the agents that are members of the group. For example:

 
<foaf:Group&gt;
 &lt;foaf:name&gt;ILRT staff&lt;/foaf:name&gt;
 &lt;foaf:member&gt;
  &lt;foaf:Person&gt;
   &lt;foaf:name&gt;Martin Poulter&lt;/foaf:name&gt;
   &lt;foaf:homepage rdf:resource="https://www.downtownmelody.com/_x/d3d3LmlscnQuYnJpcy5hYy51aw/aboutus/staff/staffprofile/?search=plmlp"/&gt;
   &lt;foaf:workplaceHomepage rdf:resource="https://www.downtownmelody.com/_x/d3d3LmlscnQuYnJpcy5hYy51aw/"/&gt;
  &lt;/foaf:Person&gt;
 &lt;/foaf:member&gt;
&lt;/foaf:Group&gt;

Behind the scenes, further RDF statements can be used to express the rules for being a member of this group. End-users of FOAF need not pay attention to these details.

Here is an example. We define a Group representing those people who are ILRT staff members (ILRT is a department at the University of Bristol). The membershipClass property connects the group (conceived of as a social entity and agent in its own right) with the class definition for those people who constitute it. In this case, the rule is that all group members are in the ILRTStaffPerson class, which is in turn populated by all those things that are a Person and which have a workplaceHomepage of https://www.downtownmelody.com/_x/d3d3LmlscnQuYnJpcy5hYy51aw/. This is typical: FOAF groups are created by specifying a sub-class of Agent (in fact usually this will be a sub-class of Person), and giving criteria for which things fall in or out of the sub-class. For this, we use the owl:onProperty and owl:hasValue properties, indicating the property/value pairs which must be true of matching agents.

&lt;!-- here we see a FOAF group described.
     each foaf group may be associated with an OWL definition 
     specifying the class of agents that constitute the group's membership --&gt;
&lt;foaf:Group&gt;
 &lt;foaf:name&gt;ILRT staff&lt;/foaf:name&gt;
 &lt;foaf:membershipClass&gt;
    &lt;owl:Class rdf:about="https://www.downtownmelody.com/_x/aWxydC5leGFtcGxlLmNvbQ/groups#ILRTStaffPerson"&gt;
     &lt;rdfs:subClassOf rdf:resource="https://www.downtownmelody.com/_x/eG1sbnMuY29t/foaf/0.1/Person"/&gt;
     &lt;rdfs:subClassOf&gt;
       &lt;owl:Restriction&gt; 
         &lt;owl:onProperty rdf:resource="https://www.downtownmelody.com/_x/eG1sbnMuY29t/foaf/0.1/workplaceHomepage"/&gt;
         &lt;owl:hasValue rdf:resource="https://www.downtownmelody.com/_x/d3d3LmlscnQuYnJpcy5hYy51aw/"/&gt;
       &lt;/owl:Restriction&gt; 
     &lt;/rdfs:subClassOf&gt;
   &lt;/owl:Class&gt;
 &lt;/foaf:membershipClass&gt;
&lt;/foaf:Group&gt;

Note that while these example OWL rules for being in the eg:ILRTStaffPerson class are based on a Person having a particular workplaceHomepage, this places no obligations on the authors of actual FOAF documents to include this information. If the information is included, then generic OWL tools may infer that some person is an eg:ILRTStaffPerson. To go the extra step and infer that some eg:ILRTStaffPerson is a member of the group whose name is "ILRT staff", tools will need some knowledge of the way FOAF deals with groups. In other words, generic OWL technology gets us most of the way, but the full Group machinery requires extra work for implimentors.

The current design names the relationship as pointing from the group, to the member. This is convenient when writing XML/RDF that encloses the members within markup that describes the group. Alternate representations of the same content are allowed in RDF, so you can write claims about the Person and the Group without having to nest either description inside the other. For (brief) example:

<foaf:Group>
 <foaf:member rdf:nodeID="martin"/>
 <!-- more about the group here -->
</foaf:Group>
<foaf:Person rdf:nodeID="martin">
  <!-- more about martin here -->
</foaf:Person>

There is a FOAF issue tracker associated with this FOAF term. A design goal is to make the most of W3C's OWL language for representing group-membership criteria, while also making it easy to leverage existing groups and datasets available online (eg. buddylists, mailing list membership lists etc). Feedback on the current design is solicited! Should we consider using SPARQL queries instead, for example?

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Class: foaf:Image

Image - An image.

Status:	stable
Properties include:	depicts thumbnail
Used with:	img thumbnail depiction
Subclass Of	Document

FOAF Vocabulary Specification 0.99

Namespace Document 14 January 2014 - Paddington Edition

Abstract

Status of This Document

Changes in version 0.99

Table of Contents

FOAF at a glance

FOAF Core

Social Web

A-Z of FOAF terms (current and archaic)

Example

1 Introduction: FOAF Basics

The Semantic Web

FOAF and the Semantic Web

The Basic Idea

What's FOAF for?

Background

FOAF and Standards

The FOAF Vocabulary Description

Evolution and Extension of FOAF

FOAF Auto-Discovery: Publishing and Linking FOAF files

FOAF cross-reference: Listing FOAF Classes and Properties

Classes and Properties (full detail)

Classes

Class: foaf:Agent

Class: foaf:Document

Class: foaf:Group

Class: foaf:Image