FOAF Vocabulary Specification 0.97

Class: foaf:Agent

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:Group

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>
 <foaf:name>ILRT staff</foaf:name>
 <foaf:member>
  <foaf:Person>
   <foaf:name>Martin Poulter</foaf:name>
   <foaf:homepage rdf:resource="http://www.ilrt.bris.ac.uk/aboutus/staff/staffprofile/?search=plmlp"/>
   <foaf:workplaceHomepage rdf:resource="http://www.ilrt.bris.ac.uk/"/>
  </foaf:Person>
 </foaf:member>
</foaf:Group>

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 http://www.ilrt.bris.ac.uk/. 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.

<!-- 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 -->
<foaf:Group>
 <foaf:name>ILRT staff</foaf:name>
 <foaf:membershipClass>
    <owl:Class rdf:about="http://ilrt.example.com/groups#ILRTStaffPerson">
     <rdfs:subClassOf rdf:resource="http://xmlns.com/foaf/0.1/Person"/>
     <rdfs:subClassOf>
       <owl:Restriction> 
         <owl:onProperty rdf:resource="http://xmlns.com/foaf/0.1/workplaceHomepage"/>
         <owl:hasValue rdf:resource="http://www.ilrt.bris.ac.uk/"/>
       </owl:Restriction> 
     </rdfs:subClassOf>
   </owl:Class>
 </foaf:membershipClass>
</foaf:Group>

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:Organization

The Organization class represents a kind of Agent corresponding to social instititutions such as companies, societies etc.

This is a more 'solid' class than Group, which allows for more ad-hoc collections of individuals. These terms, like the corresponding natural language concepts, have some overlap, but different emphasis.

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Class: foaf:Person

The Person class represents people. Something is a Person if it is a person. We don't nitpic about whether they're alive, dead, real, or imaginary. The Person class is a sub-class of the Agent class, since all people are considered 'agents' in FOAF.

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Class: foaf:Document

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:Image

The class Image is a sub-class of Document corresponding to those documents which are images.

Digital images (such as JPEG, PNG, GIF bitmaps, SVG diagrams etc.) are examples of Image.

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Class: foaf:PersonalProfileDocument

The PersonalProfileDocument class represents those things that are a Document, and that use RDF to describe properties of the person who is the maker of the document. There is just one Person described in the document, ie. the person who made it and who will be its primaryTopic.

The PersonalProfileDocument class, and FOAF's associated conventions for describing it, captures an important deployment pattern for the FOAF vocabulary. FOAF is very often used in public RDF documents made available through the Web. There is a colloquial notion that these "FOAF files" are often somebody's FOAF file. Through PersonalProfileDocument we provide a machine-readable expression of this concept, providing a basis for FOAF documents to make claims about their maker and topic.

When describing a PersonalProfileDocument it is typical (and useful) to describe its associated Person using the maker property. Anything that is a Person and that is the maker of some Document will be the primaryTopic of that Document. Although this can be inferred, it is helpful to include this information explicitly within the PersonalProfileDocument.

For example, here is a fragment of a personal profile document which describes its author explicitly:

<foaf:Person rdf:nodeID="p1">
 <foaf:name>Dan Brickley</foaf:name>
 <foaf:homepage rdf:resource="http://danbri.org/"/>
 <!-- etc... -->
</foaf:Person>

<foaf:PersonalProfileDocument rdf:about="">
   <foaf:maker rdf:nodeID="p1"/>
   <foaf:primaryTopic rdf:nodeID="p1"/>
</foaf:PersonalProfileDocument>

Note that a PersonalProfileDocument will have some representation as RDF. Typically this will be in W3C's RDF/XML syntax, however we leave open the possibility for the use of other notations, or representational conventions including automated transformations from HTML (GRDDL spec for one such technique).

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Class: foaf:LabelProperty

A LabelProperty is any RDF property with texual values that serve as labels.

Any property that is a LabelProperty is effectively a sub-property of rdfs:label. This utility class provides an alternate means of expressing this idea, in a way that may help with OWL 2.0 DL compatibility.

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Class: foaf:OnlineAccount

The OnlineAccount class represents the provision of some form of online service, by some party (indicated indirectly via a accountServiceHomepage) to some Agent. The account property of the agent is used to indicate accounts that are associated with the agent.

See OnlineChatAccount for an example. Other sub-classes include OnlineEcommerceAccount and OnlineGamingAccount.

One deployment style for this construct is to use URIs for well-known documents (or other entities) that strongly embody the account-holding relationship; for example, user profile pages on social network sites. This has the advantage of providing URIs that are likely to be easy to link with other information, but means that the instances of this class should not be considered 'accounts' in the abstract or business sense of a 'contract'.

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Class: foaf:OnlineChatAccount

A OnlineChatAccount is a OnlineAccount devoted to chat / instant messaging. The account may offer other services too; FOAF's sub-classes of OnlineAccount are not mutually disjoint.

This is a generalization of the FOAF Chat ID properties, jabberID, aimChatID, skypeID, msnChatID, icqChatID and yahooChatID.

Unlike those simple properties, OnlineAccount and associated FOAF terms allows us to describe a great variety of online accounts, without having to anticipate them in the FOAF vocabulary.

For example, here is a description of an IRC chat account, specific to the Freenode IRC network:

<foaf:Person>
  <foaf:name>Dan Brickley</foaf:name>
  <foaf:account>
    <foaf:OnlineAccount>
      <rdf:type rdf:resource="http://xmlns.com/foaf/0.1/OnlineChatAccount"/>
      <foaf:accountServiceHomepage 
               rdf:resource="http://www.freenode.net/"/>
      <foaf:accountName>danbri</foaf:accountName>
    </foaf:OnlineAccount>
  </foaf:account>
</foaf:Person>

Note that it may be impolite to carelessly reveal someone else's chat identifier (which might also serve as an indicate of email address) As with email, there are privacy and anti-SPAM considerations. FOAF does not currently provide a way to represent an obfuscated chat ID (ie. there is no parallel to the mbox / mbox_sha1sum mapping).

In addition to the generic OnlineAccount and OnlineChatAccount mechanisms, FOAF also provides several convenience chat ID properties (jabberID, aimChatID, icqChatID, msnChatID,yahooChatID, skypeID). These serve as as a shorthand for some common cases; their use may not always be appropriate.

We should specify some mappings between the abbreviated and full representations of Jabber, AIM, MSN, ICQ, Yahoo! and MSN chat accounts. This has been done for skypeID. This requires us to identify an appropriate accountServiceHomepage for each. If we wanted to make the OnlineAccount mechanism even more generic, we could invent a relationship that holds between a OnlineAccount instance and a convenience property. To continue the example above, we could describe how Freenode could define a property 'fn:freenodeChatID' corresponding to Freenode online accounts.

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Class: foaf:OnlineEcommerceAccount

A OnlineEcommerceAccount is a OnlineAccount devoted to buying and/or selling of goods, services etc. Examples include Amazon, eBay, PayPal, thinkgeek, etc.

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Class: foaf:OnlineGamingAccount

A OnlineGamingAccount is a OnlineAccount devoted to online gaming.

Examples might include EverQuest, Xbox live, Neverwinter Nights, etc., as well as older text-based systems (MOOs, MUDs and suchlike).

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Class: foaf:Project

The Project class represents the class of things that are 'projects'. These may be formal or informal, collective or individual. It is often useful to indicate the homepage of a Project.

Further work is needed to specify the connections between this class and the FOAF properties currentProject and pastProject.

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Property: foaf:homepage

The homepage property relates something to a homepage about it.

Many kinds of things have homepages. FOAF allows a thing to have multiple homepages, but constrains homepage so that there can be only one thing that has any particular homepage.

A 'homepage' in this sense is a public Web document, typically but not necessarily available in HTML format. The page has as a topic the thing whose homepage it is. The homepage is usually controlled, edited or published by the thing whose homepage it is; as such one might look to a homepage for information on its owner from its owner. This works for people, companies, organisations etc.

The homepage property is a sub-property of the more general page property for relating a thing to a page about that thing. See also topic, the inverse of the page property.

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Property: foaf:made

The made property relates a Agent to something made by it. As such it is an inverse of the maker property, which relates a thing to something that made it. See made for more details on the relationship between these FOAF terms and related Dublin Core vocabulary.

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Property: foaf:maker

The maker property relates something to a Agent that made it. As such it is an inverse of the made property.

The name (or other rdfs:label) of the maker of something can be described as the dc:creator of that thing.

For example, if the thing named by the URI http://danbri.org/ has a maker that is a Person whose name is 'Dan Brickley', we can conclude that http://danbri.org/ has a dc:creator of 'Dan Brickley'.

FOAF descriptions are encouraged to use dc:creator only for simple textual names, and to use maker to indicate creators, rather than risk confusing creators with their names. This follows most Dublin Core usage. See UsingDublinCoreCreator for details.

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Property: foaf:mbox

The mbox property is a relationship between the owner of a mailbox and a mailbox. These are typically identified using the mailto: URI scheme (see RFC 2368).

Note that there are many mailboxes (eg. shared ones) which are not the mbox of anyone. Furthermore, a person can have multiple mbox properties.

In FOAF, we often see mbox used as an indirect way of identifying its owner. This works even if the mailbox is itself out of service (eg. 10 years old), since the property is defined in terms of its primary owner, and doesn't require the mailbox to actually be being used for anything.

Many people are wary of sharing information about their mailbox addresses in public. To address such concerns whilst continuing the FOAF convention of indirectly identifying people by referring to widely known properties, FOAF also provides the mbox_sha1sum mechanism, which is a relationship between a person and the value you get from passing a mailbox URI to the SHA1 mathematical function.

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Property: foaf:member

The member property relates a Group to a Agent that is a member of that group.

See Group for details and examples.

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Property: foaf:aimChatID

The aimChatID property relates a Agent to a textual identifier ('screenname') assigned to them in the AOL Instant Messanger (AIM) system. See AOL's AIM site for more details of AIM and AIM screennames. The iChat tools from Apple also make use of AIM identifiers.

See OnlineChatAccount (and OnlineAccount) for a more general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:currentProject

A currentProject relates a Person to a Document indicating some collaborative or individual undertaking. This relationship indicates that the Person has some active role in the project, such as development, coordination, or support.

When a Person is no longer involved with a project, or perhaps is inactive for some time, the relationship becomes a pastProject.

If the Person has stopped working on a project because it has been completed (successfully or otherwise), pastProject is applicable. In general, currentProject is used to indicate someone's current efforts (and implied interests, concerns etc.), while pastProject describes what they've previously been doing.

Note that this property requires further work. There has been confusion about whether it points to a thing (eg. something you've made; a homepage for a project, ie. a Document or to instances of the class Project, which might themselves have a homepage. In practice, it seems to have been used in a similar way to interest, referencing homepages of ongoing projects.

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Property: foaf:depiction

The depiction property is a relationship between a thing and an Image that depicts it. As such it is an inverse of the depicts relationship.

A common use of depiction (and depicts) is to indicate the contents of a digital image, for example the people or objects represented in an online photo gallery.

Extensions to this basic idea include 'Co-Depiction' (social networks as evidenced in photos), as well as richer photo metadata through the mechanism of using SVG paths to indicate the regions of an image which depict some particular thing. See 'Annotating Images With SVG' for tools and details.

The basic notion of 'depiction' could also be extended to deal with multimedia content (video clips, audio), or refined to deal with corner cases, such as pictures of pictures etc.

The depiction property is a super-property of the more specific property img, which is used more sparingly. You stand in a depiction relation to any Image that depicts you, whereas img is typically used to indicate a few images that are particularly representative.

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Property: foaf:depicts

The depicts property is a relationship between a Image and something that the image depicts. As such it is an inverse of the depiction relationship. See depiction for further notes.

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Property: foaf:familyName

The familyName property is provided (alongside givenName) for use when describing parts of people's names. Although these concepts do not capture the full range of personal naming styles found world-wide, they are commonly used and have some value.

There is also a simple name property.

Support is also provided for the more archaic and culturally varying terminology of firstName and lastName.

See the issue tracker for design discussions, status and ongoing work on rationalising the FOAF naming machinery.

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Property: foaf:firstName

The firstName property is provided (alongside lastName) as a mechanism to support legacy data that cannot be easily interpreted in terms of the (otherwise preferred) familyName and givenName properties. The concepts of 'first' and 'last' names do not work well across cultural and linguistic boundaries; however they are widely used in addressbooks and databases.

See the issue tracker for design discussions, status and ongoing work on rationalising the FOAF naming machinery.

There is also a simple name property.

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Property: foaf:gender

The gender property relates a Agent (typically a Person) to a string representing its gender. In most cases the value will be the string 'female' or 'male' (in lowercase without surrounding quotes or spaces). Like all FOAF properties, there is in general no requirement to use gender in any particular document or description. Values other than 'male' and 'female' may be used, but are not enumerated here. The gender mechanism is not intended to capture the full variety of biological, social and sexual concepts associated with the word 'gender'.

Anything that has a gender property will be some kind of Agent. However there are kinds of Agent to which the concept of gender isn't applicable (eg. a Group). FOAF does not currently include a class corresponding directly to "the type of thing that has a gender". At any point in time, a Agent has at most one value for gender. FOAF does not treat gender as a static property; the same individual may have different values for this property at different times.

Note that FOAF's notion of gender isn't defined biologically or anatomically - this would be tricky since we have a broad notion that applies to all Agents (including robots - eg. Bender from Futurama is 'male'). As stressed above, FOAF's notion of gender doesn't attempt to encompass the full range of concepts associated with human gender, biology and sexuality. As such it is a (perhaps awkward) compromise between the clinical and the social/psychological. In general, a person will be the best authority on their gender. Feedback on this design is particularly welcome (via the FOAF mailing list, foaf-dev). We have tried to be respectful of diversity without attempting to catalogue or enumerate that diversity.

This may also be a good point for a periodic reminder: as with all FOAF properties, documents that use 'gender' will on occassion be innacurate, misleading or outright false. FOAF, like all open means of communication, supports lying. Application authors using FOAF data should always be cautious in their presentation of unverified information, but be particularly sensitive to issues and risks surrounding sex and gender (including privacy and personal safety concerns). Designers of FOAF-based user interfaces should be careful to allow users to omit gender when describing themselves and others, and to allow at least for values other than 'male' and 'female' as options. Users of information conveyed via FOAF (as via information conveyed through mobile phone text messages, email, Internet chat, HTML pages etc.) should be skeptical of unverified information.

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Property: foaf:givenName

The givenName property is provided (alongside familyName) for use when describing parts of people's names. Although these concepts do not capture the full range of personal naming styles found world-wide, they are commonly used and have some value.

There is also a simple name property.

Support is also provided for the more archaic and culturally varying terminology of firstName and lastName.

See the issue tracker for design discussions, status and ongoing work on rationalising the FOAF naming machinery.

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Property: foaf:icqChatID

The icqChatID property relates a Agent to a textual identifier assigned to them in the ICQ Chat system. See the icq chat site for more details of the 'icq' service. Their "What is ICQ?" document provides a basic overview, while their "About Us page notes that ICQ has been acquired by AOL. Despite the relationship with AOL, ICQ is at the time of writing maintained as a separate identity from the AIM brand (see aimChatID).

See OnlineChatAccount (and OnlineAccount) for a more general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:img

The img property relates a Person to a Image that represents them. Unlike its super-property depiction, we only use img when an image is particularly representative of some person. The analogy is with the image(s) that might appear on someone's homepage, rather than happen to appear somewhere in their photo album.

Unlike the more general depiction property (and its inverse, depicts), the img property is only used with representations of people (ie. instances of Person). So you can't use it to find pictures of cats, dogs etc. The basic idea is to have a term whose use is more restricted than depiction so we can have a useful way of picking out a reasonable image to represent someone. FOAF defines img as a sub-property of depiction, which means that the latter relationship is implied whenever two things are related by the former.

Note that img does not have any restrictions on the dimensions, colour depth, format etc of the Image it references.

Terminology: note that img is a property (ie. relationship), and that code:Image is a similarly named class (ie. category, a type of thing). It might have been more helpful to call img 'mugshot' or similar; instead it is named by analogy to the HTML IMG element.

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Property: foaf:interest

The interest property represents an interest of a Agent, through indicating a Document whose topic(s) broadly characterises that interest.

For example, we might claim that a person or group has an interest in RDF by saying they stand in a interest relationship to the RDF home page. Loosly, such RDF would be saying "this agent is interested in the topic of this page".

Uses of interest include a variety of filtering and resource discovery applications. It could be used, for example, to help find answers to questions such as "Find me members of this organisation with an interest in XML who have also contributed to CPAN)".

This approach to characterising interests is intended to compliment other mechanisms (such as the use of controlled vocabulary). It allows us to use a widely known set of unique identifiers (Web page URIs) with minimal pre-coordination. Since URIs have a controlled syntax, this makes data merging much easier than the use of free-text characterisations of interest.

Note that interest does not imply expertise, and that this FOAF term provides no support for characterising levels of interest: passing fads and lifelong quests are both examples of someone's interest. Describing interests in full is a complex undertaking; interest provides one basic component of FOAF's approach to these problems.

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Property: foaf:isPrimaryTopicOf

The isPrimaryTopicOf property relates something to a document that is mainly about it.

The isPrimaryTopicOf property is inverse functional: for any document that is the value of this property, there is at most one thing in the world that is the primary topic of that document. This is useful, as it allows for data merging, as described in the documentation for its inverse, primaryTopic.

page is a super-property of isPrimaryTopicOf. The change of terminology between the two property names reflects the utility of 'primaryTopic' and its inverse when identifying things. Anything that has an isPrimaryTopicOf relation to some document X, also has a page relationship to it.

Note that homepage, is a sub-property of both page and isPrimarySubjectOf. The awkwardly named isPrimarySubjectOf is less specific, and can be used with any document that is primarily about the thing of interest (ie. not just on homepages).

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Property: foaf:jabberID

The jabberID property relates a Agent to a textual identifier assigned to them in the Jabber messaging system. See the Jabber site for more information about the Jabber protocols and tools.

Jabber, unlike several other online messaging systems, is based on an open, publically documented protocol specification, and has a variety of open source implementations. Jabber IDs can be assigned to a variety of kinds of thing, including software 'bots', chat rooms etc. For the purposes of FOAF, these are all considered to be kinds of Agent (ie. things that do stuff). The uses of Jabber go beyond simple IM chat applications. The jabberID property is provided as a basic hook to help support RDF description of Jabber users and services.

See OnlineChatAccount (and OnlineAccount) for a more general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:knows

The knows property relates a Person to another Person that he or she knows.

We take a broad view of 'knows', but do require some form of reciprocated interaction (ie. stalkers need not apply). Since social attitudes and conventions on this topic vary greatly between communities, counties and cultures, it is not appropriate for FOAF to be overly-specific here.

If someone knows a person, it would be usual for the relation to be reciprocated. However this doesn't mean that there is any obligation for either party to publish FOAF describing this relationship. A knows relationship does not imply friendship, endorsement, or that a face-to-face meeting has taken place: phone, fax, email, and smoke signals are all perfectly acceptable ways of communicating with people you know.

You probably know hundreds of people, yet might only list a few in your public FOAF file. That's OK. Or you might list them all. It is perfectly fine to have a FOAF file and not list anyone else in it at all. This illustrates the Semantic Web principle of partial description: RDF documents rarely describe the entire picture. There is always more to be said, more information living elsewhere in the Web (or in our heads...).

Since knows is vague by design, it may be suprising that it has uses. Typically these involve combining other RDF properties. For example, an application might look at properties of each weblog that was made by someone you "knows". Or check the newsfeed of the online photo archive for each of these people, to show you recent photos taken by people you know.

To provide additional levels of representation beyond mere 'knows', FOAF applications can do several things.

They can use more precise relationships than knows to relate people to people. The original FOAF design included two of these ('knowsWell','friend') which we removed because they were somewhat awkward to actually use, bringing an inappopriate air of precision to an intrinsically vague concept. Other extensions have been proposed, including Eric Vitiello's Relationship module for FOAF.

In addition to using more specialised inter-personal relationship types (eg rel:acquaintanceOf etc) it is often just as good to use RDF descriptions of the states of affairs which imply particular kinds of relationship. So for example, two people who have the same value for their workplaceHomepage property are typically colleagues. We don't (currently) clutter FOAF up with these extra relationships, but the facts can be written in FOAF nevertheless. Similarly, if there exists a Document that has two people listed as its makers, then they are probably collaborators of some kind. Or if two people appear in 100s of digital photos together, there's a good chance they're friends and/or colleagues.

So FOAF is quite pluralistic in its approach to representing relationships between people. FOAF is built on top of a general purpose machine language for representing relationships (ie. RDF), so is quite capable of representing any kinds of relationship we care to add. The problems are generally social rather than technical; deciding on appropriate ways of describing these interconnections is a subtle art.

Perhaps the most important use of knows is, alongside the rdfs:seeAlso property, to connect FOAF files together. Taken alone, a FOAF file is somewhat dull. But linked in with 1000s of other FOAF files it becomes more interesting, with each FOAF file saying a little more about people, places, documents, things... By mentioning other people (via knows or other relationships), and by providing an rdfs:seeAlso link to their FOAF file, you can make it easy for FOAF indexing tools ('scutters') to find your FOAF and the FOAF of the people you've mentioned. And the FOAF of the people they mention, and so on. This makes it possible to build FOAF aggregators without the need for a centrally managed directory of FOAF files...

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Property: foaf:logo

The logo property is used to indicate a graphical logo of some kind. It is probably underspecified...

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Property: foaf:mbox_sha1sum

A mbox_sha1sum of a Person is a textual representation of the result of applying the SHA1 mathematical functional to a 'mailto:' identifier (URI) for an Internet mailbox that they stand in a mbox relationship to.

In other words, if you have a mailbox (mbox) but don't want to reveal its address, you can take that address and generate a mbox_sha1sum representation of it. Just as a mbox can be used as an indirect identifier for its owner, we can do the same with mbox_sha1sum since there is only one Person with any particular value for that property.

Many FOAF tools use mbox_sha1sum in preference to exposing mailbox information. This is usually for privacy and SPAM-avoidance reasons. Other relevant techniques include the use of PGP encryption (see Edd Dumbill's documentation) and the use of FOAF-based whitelists for mail filtering.

Code examples for SHA1 in C#, Java, PHP, Perl and Python can be found in Sam Ruby's weblog entry. Remember to include the 'mailto:' prefix, but no trailing whitespace, when computing a mbox_sha1sum property.

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Property: foaf:msnChatID

The msnChatID property relates a Agent to a textual identifier assigned to them in the Microsoft online chat system originally known as 'MSN', and now Windows Live Messenger. See the Microsoft mesenger and Windows Live ID sites for more details.

See OnlineChatAccount (and OnlineAccount) for a more general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:myersBriggs

The myersBriggs property represents the Myers Briggs (MBTI) approach to personality taxonomy. It is included in FOAF as an example of a property that takes certain constrained values, and to give some additional detail to the FOAF files of those who choose to include it. The myersBriggs property applies only to the Person class; wherever you see it, you can infer it is being applied to a person.

The myersBriggs property is interesting in that it illustrates how FOAF can serve as a carrier for various kinds of information, without necessarily being commited to any associated worldview. Not everyone will find myersBriggs (or star signs, or blood types, or the four humours) a useful perspective on human behaviour and personality. The inclusion of a Myers Briggs property doesn't indicate that FOAF endorses the underlying theory, any more than the existence of weblog is an endorsement of soapboxes.

The values for myersBriggs are the following 16 4-letter textual codes: ESTJ, INFP, ESFP, INTJ, ESFJ, INTP, ENFP, ISTJ, ESTP, INFJ, ENFJ, ISTP, ENTJ, ISFP, ENTP, ISFJ. If multiple of these properties are applicable, they are represented by applying multiple properties to a person.

For further reading on MBTI, see various online sources (eg. this article). There are various online sites which offer quiz-based tools for determining a person's MBTI classification. The owners of the MBTI trademark have probably not approved of these.

This FOAF property suggests some interesting uses, some of which could perhaps be used to test the claims made by proponents of the MBTI (eg. an analysis of weblog postings filtered by MBTI type). However it should be noted that MBTI FOAF descriptions are self-selecting; MBTI categories may not be uniformly appealing to the people they describe. Further, there is probably a degree of cultural specificity implicit in the assumptions made by many questionaire-based MBTI tools; the MBTI system may not make sense in cultural settings beyond those it was created for.

See also Cory Caplinger's summary table or the RDFWeb article, FOAF Myers Briggs addition for further background and examples.

Note: Myers Briggs Type Indicator and MBTI are registered trademarks of Consulting Psychologists Press Inc. Oxford Psycholgists Press Ltd has exclusive rights to the trademark in the UK.

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Property: foaf:name

The name of something is a simple textual string.

XML language tagging may be used to indicate the language of the name. For example:

FOAF provides some other naming constructs. While foaf:name does not explicitly represent name substructure (family vs given etc.) it does provide a basic level of interoperability. See the issue tracker for status of work on this issue.

The name property, like all RDF properties with a range of rdfs:Literal, may be used with XMLLiteral datatyped values (multiple names are acceptable whether they are in the same langauge or not). XMLLiteral usage is not yet widely adopted. Feedback on this aspect of the FOAF design is particularly welcomed.

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Property: foaf:nick

The nick property relates a Person to a short (often abbreviated) nickname, such as those use in IRC chat, online accounts, and computer logins.

This property is necessarily vague, because it does not indicate any particular naming control authority, and so cannot distinguish a person's login from their (possibly various) IRC nicknames or other similar identifiers. However it has some utility, since many people use the same string (or slight variants) across a variety of such environments.

For specific controlled sets of names (relating primarily to Instant Messanger accounts), FOAF provides some convenience properties: jabberID, aimChatID, msnChatID and icqChatID. Beyond this, the problem of representing such accounts is not peculiar to Instant Messanging, and it is not scaleable to attempt to enumerate each naming database as a distinct FOAF property. The OnlineAccount term (and supporting vocabulary) are provided as a more verbose and more expressive generalisation of these properties.

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Property: foaf:page

The page property relates a thing to a document about that thing.

As such it is an inverse of the topic property, which relates a document to a thing that the document is about.

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Property: foaf:pastProject

After a Person is no longer involved with a currentProject, or has been inactive for some time, a pastProject relationship can be used. This indicates that the Person was involved with the described project at one point.

If the Person has stopped working on a project because it has been completed (successfully or otherwise), pastProject is applicable. In general, currentProject is used to indicate someone's current efforts (and implied interests, concerns etc.), while pastProject describes what they've previously been doing.

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Property: foaf:phone

The phone of something is a phone, typically identified using the tel: URI scheme.

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Property: foaf:plan

The plan property provides a space for a Person to hold some arbitrary content that would appear in a traditional '.plan' file. The plan file was stored in a user's home directory on a UNIX machine, and displayed to people when the user was queried with the finger utility.

A plan file could contain anything. Typical uses included brief comments, thoughts, or remarks on what a person had been doing lately. Plan files were also prone to being witty or simply osbscure. Others may be more creative, writing any number of seemingly random compositions in their plan file for people to stumble upon.

See History of the Finger Protocol by Rajiv Shah for more on this piece of Internet history. The geekcode property may also be of interest.

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Property: foaf:primaryTopic

The primaryTopic property relates a document to the main thing that the document is about.

The primaryTopic property is functional: for any document it applies to, it can have at most one value. This is useful, as it allows for data merging. In many cases it may be difficult for third parties to determine the primary topic of a document, but in a useful number of cases (eg. descriptions of movies, restaurants, politicians, ...) it should be reasonably obvious. Documents are very often the most authoritative source of information about their own primary topics, although this cannot be guaranteed since documents cannot be assumed to be accurate, honest etc.

It is an inverse of the isPrimaryTopicOf property, which relates a thing to a document primarily about that thing. The choice between these two properties is purely pragmatic. When describing documents, we use primaryTopic former to point to the things they're about. When describing things (people etc.), it is useful to be able to directly cite documents which have those things as their main topic - so we use isPrimaryTopicOf. In this way, Web sites such as Wikipedia or NNDB can provide indirect identification for the things they have descriptions of.

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Property: foaf:publications

The publications property indicates a Document listing (primarily in human-readable form) some publications associated with the Person. Such documents are typically published alongside one's homepage.

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Property: foaf:schoolHomepage

The schoolHomepage property relates a Person to a Document that is the homepage of a School that the person attended.

FOAF does not (currently) define a class for 'School' (if it did, it would probably be as a sub-class of Organization). The original application area for schoolHomepage was for 'schools' in the British-English sense; however American-English usage has dominated, and it is now perfectly reasonable to describe Universities, Colleges and post-graduate study using schoolHomepage.

This very basic facility provides a basis for a low-cost, decentralised approach to classmate-reunion and suchlike. Instead of requiring a central database, we can use FOAF to express claims such as 'I studied here' simply by mentioning a school's homepage within FOAF files. Given the homepage of a school, it is easy for FOAF aggregators to lookup this property in search of people who attended that school.

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Property: foaf:surname

A number of naming constructs are under development to provide naming substructure; draft properties include firstName, givenName, and surname. These are not currently stable or consistent; see the issue tracker for design discussions, status and ongoing work on rationalising the FOAF naming machinery.

There is also a simple name property.

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Property: foaf:thumbnail

The thumbnail property is a relationship between a full-size Image and a smaller, representative Image that has been derrived from it.

It is typical in FOAF to express img and depiction relationships in terms of the larger, 'main' (in some sense) image, rather than its thumbnail(s). A thumbnail might be clipped or otherwise reduced such that it does not depict everything that the full image depicts. Therefore FOAF does not specify that a thumbnail depicts everything that the image it is derrived from depicts. However, FOAF does expect that anything depicted in the thumbnail will also be depicted in the source image.

A thumbnail is typically small enough that it can be loaded and viewed quickly before a viewer decides to download the larger version. They are often used in online photo gallery applications.

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Property: foaf:tipjar

The tipjar property relates an Agent to a Document that describes some mechanisms for paying or otherwise rewarding that agent.

The tipjar property was created following discussions about simple, lightweight mechanisms that could be used to encourage rewards and payment for content exchanged online. An agent's tipjar page(s) could describe informal ("Send me a postcard!", "here's my book, music and movie wishlist") or formal (machine-readable micropayment information) information about how that agent can be paid or rewarded. The reward is not associated with any particular action or content from the agent concerned. A link to a service such as PayPal is the sort of thing we might expect to find in a tipjar document.

Note that the value of a tipjar property is just a document (which can include anchors into HTML pages). We expect, but do not currently specify, that this will evolve into a hook for finding more machine-readable information to support payments, rewards. The OnlineAccount machinery is also relevant, although the information requirements for automating payments are not currently clear.

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Property: foaf:topic

The topic property relates a document to a thing that the document is about.

As such it is an inverse of the page property, which relates a thing to a document about that thing.

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Property: foaf:topic_interest

The topic_interest property is generally found to be confusing and ill-defined and is a candidate for removal. The goal was to be link a person to some thing that is a topic of their interests (rather than, per interest to a page that is about such a topic).

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Property: foaf:weblog

The weblog property relates a Agent to a weblog of that agent.

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Property: foaf:workInfoHomepage

The workInfoHomepage of a Person is a Document that describes their work. It is generally (but not necessarily) a different document from their homepage, and from any workplaceHomepage(s) they may have.

The purpose of this property is to distinguish those pages you often see, which describe someone's professional role within an organisation or project. These aren't really homepages, although they share some characterstics.

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Property: foaf:workplaceHomepage

The workplaceHomepage of a Person is a Document that is the homepage of a Organization that they work for.

By directly relating people to the homepages of their workplace, we have a simple convention that takes advantage of a set of widely known identifiers, while taking care not to confuse the things those identifiers identify (ie. organizational homepages) with the actual organizations those homepages describe.

<foaf:Person>
 <foaf:name>Dan Brickley</foaf:name>
 <foaf:workplaceHomepage rdf:resource="http://www.w3.org/"/>
</foaf:Person>

Note that several other FOAF properties work this way; schoolHomepage is the most similar. In general, FOAF often indirectly identifies things via Web page identifiers where possible, since these identifiers are widely used and known. FOAF does not currently have a term for the name of the relation (eg. "workplace") that holds between a Person and an Organization that they work for.

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Property: foaf:yahooChatID

The yahooChatID property relates a Agent to a textual identifier assigned to them in the Yahoo online Chat system. See Yahoo's the Yahoo! Chat site for more details of their service. Yahoo chat IDs are also used across several other Yahoo services, including email and Yahoo! Groups.

See OnlineChatAccount (and OnlineAccount) for a more general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:account

The account property relates a Agent to an OnlineAccount for which they are the sole account holder. See OnlineAccount for usage details.

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Property: foaf:accountName

The accountName property of a OnlineAccount is a textual representation of the account name (unique ID) associated with that account.

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Property: foaf:accountServiceHomepage

The accountServiceHomepage property indicates a relationship between a OnlineAccount and the homepage of the supporting service provider.

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Property: foaf:age

The age property is a relationship between a Agent and an integer string representing their age in years. See also birthday.

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Property: foaf:based_near

The based_near relationship relates two "spatial things" (anything that can be somewhere), the latter typically described using the geo:lat / geo:long geo-positioning vocabulary (See GeoInfo in the W3C semweb wiki for details). This allows us to say describe the typical latitute and longitude of, say, a Person (people are spatial things - they can be places) without implying that a precise location has been given.

We do not say much about what 'near' means in this context; it is a 'rough and ready' concept. For a more precise treatment, see GeoOnion vocab design discussions, which are aiming to produce a more sophisticated vocabulary for such purposes.

FOAF files often make use of the contact:nearestAirport property. This illustrates the distinction between FOAF documents (which may make claims using any RDF vocabulary) and the core FOAF vocabulary defined by this specification. For further reading on the use of nearestAirport see UsingContactNearestAirport in the FOAF wiki.

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Property: foaf:birthday

The birthday property is a relationship between a Agent and a string representing the month and day in which they were born (Gregorian calendar). See BirthdayIssue for details of related properties that can be used to describe such things in more flexible ways.

See also age.

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Property: foaf:dnaChecksum

The dnaChecksum property is mostly a joke, but also a reminder that there will be lots of different identifying properties for people, some of which we might find disturbing.

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Property: foaf:lastName

The lastName property is provided (alongside firstName) as a mechanism to support legacy data that cannot be easily interpreted in terms of the (otherwise preferred) familyName and givenName properties. The concepts of 'first' and 'last' names do not work well across cultural and linguistic boundaries; however they are widely used in addressbooks and databases.

See the issue tracker for design discussions, status and ongoing work on rationalising the FOAF naming machinery.

There is also a simple name property.

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Property: foaf:membershipClass

The membershipClass property relates a Group to an RDF class representing a sub-class of Agent whose instances are all the agents that are a member of the Group.

See Group for details and examples.

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Property: foaf:openid

A openid is a property of a Agent that associates it with a document that can be used as an indirect identifier in the manner of the OpenID "Identity URL". As the OpenID 1.1 specification notes, OpenID itself"does not provide any mechanism to exchange profile information, though Consumers of an Identity can learn more about an End User from any public, semantically interesting documents linked thereunder (FOAF, RSS, Atom, vCARD, etc.)". In this way, FOAF and OpenID complement each other; neither provides a stand-alone approach to online "trust", but combined they can address interesting parts of this larger problem space.

The openid property is "inverse functional", meaning that anything that is the foaf:openid of something, is the openid of no more than one thing. FOAF is agnostic as to whether there are (according to the relevant OpenID specifications) OpenID URIs that are equally associated with multiple Agents. FOAF offers sub-classes of Agent, ie. Organization and Group, that allow for such scenarios to be consistent with the notion that any foaf:openid is the foaf:openid of just one Agent.

FOAF does not mandate any particular URI scheme for use as openid values. The OpenID 1.1 specification includes a delegation model that is often used to allow a weblog or homepage document to also serve in OpenID authentication via "link rel" HTML markup. This deployment model provides a convenient connection to FOAF, since a similar technique is used for FOAF autodiscovery in HTML. A single document can, for example, serve both as a homepage and an OpenID identity URL.

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Property: foaf:sha1

The sha1 property relates a Document to the textual form of a SHA1 hash of (some representation of) its contents.

The design for this property is neither complete nor coherent. The Document class is currently used in a way that allows multiple instances at different URIs to have the 'same' contents (and hence hash). If sha1 is an owl:InverseFunctionalProperty, we could deduce that several such documents were the self-same thing. A more careful design is needed, which distinguishes documents in a broad sense from byte sequences.

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Property: foaf:skypeID

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Property: foaf:status

status is a short textual string expressing what the user is happy for the general public (normally) to know about their current activity. mood, location, etc.

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Property: foaf:title

This property is a candidate for deprecation in favour of 'honorificPrefix' following Portable Contacts usage. See the FOAF Issue Tracker.

The approriate values for title are not formally constrained, and will vary across community and context. Values such as 'Mr', 'Mrs', 'Ms', 'Dr' etc. are expected.

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Property: foaf:family_name

This property is considered an archaic spelling of familyName.

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Property: foaf:fundedBy

The fundedBy property relates something to something else that has provided funding for it.

This property is tentatively considered archaic usage, unless we hear about positive implementation experience.

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Property: foaf:geekcode

The geekcode property is used to represent a 'Geek Code' for some Person.

See the Wikipedia entry for details of the code, which provides a somewhat frivolous and willfully obscure mechanism for characterising technical expertise, interests and habits. The geekcode property is not bound to any particular version of the code.

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Property: foaf:givenname

The givenName property is provided (alongside familyName) for use when describing parts of people's names. Although these concepts do not capture the full range of personal naming styles found world-wide, they are commonly used and have some value.

There is also a simple name property.

Support is also provided for the more archaic and culturally varying terminology of firstName and lastName.

See the issue tracker for design discussions, status and ongoing work on rationalising the FOAF naming machinery.

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Property: foaf:holdsAccount

This property is considered archaic usage. It is generally better to use account instead.

The holdsAccount property relates a Agent to an OnlineAccount for which they are the sole account holder. See OnlineAccount for usage details.

This property is equivalent to the account property, which was introduced primarily to provide simpler naming for the same idea.

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Property: foaf:theme

This property is considered archaic usage, and is not currently recommended for usage.

The theme property is rarely used and under-specified. The intention was to use it to characterise interest / themes associated with projects and groups. Further work is needed to meet these goals.

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