Class: foaf:Agent

TheAgent class is the class of agents; things that do stuff. A well known sub-class isPerson, representing people. Other kinds of agents includeOrganization andGroup.

TheAgent class is useful in a few places in FOAF wherePerson would have been overly specific. For example, the IM chat ID properties such asjabberID are typically associated with people, but sometimes belong to software bots.

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Class: foaf:Document

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

TheImage class is a sub-class ofDocument, 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 (seesha1 for related issues).

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Class: foaf:Group

TheGroup class represents a collection of individual agents (and may itself play the role of aAgent, 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 ahomepage,name, mailing list etc.).

While aGroup has the characteristics of aAgent, it is also associated with a number of otherAgents (typically people) who constitute theGroup. FOAF provides a mechanism, themembershipClass property, which relates aGroup to a sub-class of the classAgent 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, theGroup mechanism for categorising them into groups also becomes more powerful.

While the formal description of membership criteria for aGroup maybe complex, the basic mechanism for saying that someone is in aGroup isvery simple. We simply use amember property of theGroup 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 aGroup representing those people who are ILRT staff members (ILRT is a department at the University of Bristol). ThemembershipClass 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 aPerson and which have aworkplaceHomepage of http://www.ilrt.bris.ac.uk/. This is typical: FOAF groups are created by specifying a sub-class ofAgent (in fact usually this will be a sub-class ofPerson), and giving criteria for which things fall in or out of the sub-class. For this, we use theowl:onProperty andowl: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 aPerson having a particularworkplaceHomepage, this places no obligations on the authors of actual FOAF documents to include this information. If the informationis 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 amember of the group whosename 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 fullGroup machinery requires extra work for implimentors.

The current design names the relationship as pointingfrom 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 FOAFissue tracker associated with this FOAF term. A design goal is to make the most of W3C'sOWL 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

The classImage is a sub-class ofDocument corresponding to those documents which are images.

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

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Class: foaf:Organization

TheOrganization class represents a kind ofAgent corresponding to social instititutions such as companies, societies etc.

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

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Class: foaf:Person

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

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Class: foaf:OnlineAccount

TheOnlineAccount class represents the provision of some form of online service, by some party (indicated indirectly via aaccountServiceHomepage) to someAgent. Theaccount property of the agent is used to indicate accounts that are associated with the agent.

SeeOnlineChatAccount for an example. Other sub-classes includeOnlineEcommerceAccount andOnlineGamingAccount.

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:PersonalProfileDocument

ThePersonalProfileDocument class represents thosethings that are aDocument, and that use RDF todescribe properties of the person who is themakerof the document. There is just onePerson described inthe document, ie.the person whomade it and who will be itsprimaryTopic.

ThePersonalProfileDocument class, and FOAF'sassociated conventions for describing it, captures an importantdeployment pattern for the FOAF vocabulary. FOAF is very often used inpublic RDF documents made available through the Web. There is acolloquial notion that these "FOAF files" are oftensomebody'sFOAF file. ThroughPersonalProfileDocument we providea machine-readable expression of this concept, providing a basis for FOAF documents to make claims about their maker and topic.

When describing aPersonalProfileDocument it istypical (and useful) to describe its associatedPersonusing themaker property. Anything that is aPerson and that is themaker of somePersonalProfileDocument will be theprimaryTopic ofthatDocument. Although this can be inferred, it isoften helpful to include this information explicitly within thePersonalProfileDocument.

For example, here is a fragment of a personal profile document whichdescribes 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 aPersonalProfileDocument will have somerepresentation as RDF. Typically this will be in W3C's RDF/XML syntax,however we leave open the possibility for the use of other notations, orrepresentational conventions including automated transformations fromHTML (GRDDL spec forone such technique).

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Class: foaf:Project

TheProject class represents the class of things that are 'projects'. These may be formal or informal, collective or individual. It is often useful to indicate thehomepage of aProject.

Further work is needed to specify the connections between this class and the FOAF propertiescurrentProject andpastProject.

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Class: foaf:LabelProperty

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

Any property that is aLabelProperty is effectively a sub-property of rdfs:label. This utilityclass 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:OnlineChatAccount

AOnlineChatAccount is aOnlineAccount devoted to chat / instant messaging. The account may offer other services too; FOAF's sub-classes ofOnlineAccount are not mutually disjoint.

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

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 thembox /mbox_sha1sum mapping).

In addition to the genericOnlineAccount andOnlineChatAccount 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 ofJabber,AIM,MSN,ICQ,Yahoo! andMSN chat accounts. This has been done forskypeID. This requires us to identify an appropriateaccountServiceHomepage for each. If we wanted to make theOnlineAccount mechanism even more generic, we could invent a relationship that holds between aOnlineAccount instance and a convenience property. To continue the example above, we could describe howFreenode could define a property 'fn:freenodeChatID' corresponding to Freenode online accounts.

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Class: foaf:OnlineEcommerceAccount

AOnlineEcommerceAccount is aOnlineAccount devoted to buying and/or selling of goods, services etc. Examples includeAmazon,eBay,PayPal,thinkgeek, etc.

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Class: foaf:OnlineGamingAccount

AOnlineGamingAccount is aOnlineAccount devoted to online gaming.

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

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Property: foaf:homepage

Thehomepage property relates something to a homepage about it.

Many kinds of things have homepages. FOAF allows a thing to have multiple homepages, but constrainshomepage 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 atopic 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.

Thehomepage property is a sub-property of the more generalpage property for relating a thing to a page about that thing. See alsotopic, the inverse of thepage property.

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Property: foaf:isPrimaryTopicOf

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

TheisPrimaryTopicOf property isinverse functional: forany document that is the value of this property, there is at most one thing in the worldthat 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 ofisPrimaryTopicOf. The change of terminology between the two property names reflects the utility of 'primaryTopic' and its inverse when identifying things. Anything that has anisPrimaryTopicOf relation to some document X, also has apage relationship to it.

Note thathomepage, is a sub-property of bothpage andisPrimaryTopicOf. The awkwardly namedisPrimaryTopicOf 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:knows

Theknows property relates aPerson to anotherPerson 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 someoneknows 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. Aknows 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...).

Sinceknows 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 eachweblog that wasmade 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 thanknows to relate people to people. The original FOAF design included two of these ('knowsWell','friend') which we removed because they were somewhatawkward to actually use, bringing an inappopriate air of precision to an intrinsically vague concept. Other extensions have been proposed, including Eric Vitiello'sRelationship 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 theirworkplaceHomepage 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 aDocument that has two people listed as itsmakers, 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 ofknows is, alongside therdfs: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 (viaknows or other relationships), and by providing anrdfs: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:made

Themade property relates aAgent to somethingmade by it. As such it is an inverse of themaker property, which relates a thing to something that made it. Seemade for more details on the relationship between these FOAF terms and related Dublin Core vocabulary.

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Property: foaf:maker

Themaker property relates something to aAgent thatmade it. As such it is an inverse of themade property.

Thename (or otherrdfs:label) of themaker of something can be described as thedc:creator of that thing.

For example, if the thing named by the URI http://danbri.org/ has amaker that is aPerson whosename is 'Dan Brickley', we can conclude that http://danbri.org/ has adc:creator of 'Dan Brickley'.

FOAF descriptions are encouraged to usedc:creator only for simple textual names, and to usemaker to indicate creators, rather than risk confusing creators with their names. This follows most Dublin Core usage. SeeUsingDublinCoreCreator for details.

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Property: foaf:mbox

Thembox property is a relationship between the owner of a mailbox and a mailbox. These are typically identified using the mailto: URI scheme (seeRFC 2368).

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

In FOAF, we often seembox 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 thembox_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

Themember property relates aGroup to aAgent that is a member of that group.

SeeGroup for details and examples.

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Property: foaf:page

Thepage property relates a thing to a document about that thing.

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

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Property: foaf:primaryTopic

TheprimaryTopic property relates a document to themain thing that the document is about.

TheprimaryTopic property isfunctional: forany document it applies to, it can have at most one value. This isuseful, as it allows for data merging. In many cases it may be difficultfor third parties to determine the primary topic of a document, but ina useful number of cases (eg. descriptions of movies, restaurants,politicians, ...) it should be reasonably obvious. Documents are veryoften the most authoritative source of information about their ownprimary topics, although this cannot be guaranteed since documents cannot beassumed to be accurate, honest etc.

It is an inverse of theisPrimaryTopicOf property, which relates a thing to a documentprimarily about that thing. The choice between these two properties is purely pragmatic. When describing documents, we useprimaryTopic 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 useisPrimaryTopicOf. In this way, Web sites such asWikipedia orNNDB can provide indirect identification for the things they have descriptions of.

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Property: foaf:weblog

Theweblog property relates aAgent to a weblog of that agent.

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Property: foaf:account

Theaccount property relates aAgent to anOnlineAccount for which they are the sole account holder. SeeOnlineAccount for usage details.

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Property: foaf:accountName

TheaccountName property of aOnlineAccount is a textual representation of the account name (unique ID) associated with that account.

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Property: foaf:accountServiceHomepage

TheaccountServiceHomepage property indicates a relationship between aOnlineAccount and the homepage of the supporting service provider.

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Property: foaf:aimChatID

TheaimChatID property relates aAgent to a textual identifier ('screenname') assigned to them in the AOL Instant Messanger (AIM) system. See AOL'sAIM site for more details of AIM and AIM screennames. TheiChat tools fromApple also make use of AIM identifiers.

SeeOnlineChatAccount (andOnlineAccount) for amore general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:based_near

Thebased_near relationship relates two "spatial things"(anything that canbe somewhere), the latter typicallydescribed using the geo:lat / geo:longgeo-positioning vocabulary(SeeGeoInfo in the W3C semwebwiki 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, seeGeoOnion vocab designdiscussions, which are aiming to produce a more sophisticated vocabulary for such purposes.

FOAF files often make use of thecontact:nearestAirport property. Thisillustrates the distinction between FOAF documents (which may make claims usingany RDFvocabulary) and the core FOAF vocabulary defined by this specification. For further reading onthe use ofnearestAirport seeUsingContactNearestAirport in the FOAF wiki.

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Property: foaf:currentProject

AcurrentProject relates aPersonto aDocument indicating some collaborative orindividual undertaking. This relationshipindicates that thePerson has some active role in theproject, such as development, coordination, or support.

When aPerson is no longer involved with a project, orperhaps is inactive for some time, the relationship becomes apastProject.

If thePerson has stopped working on a project because ithas been completed (successfully or otherwise),pastProject isapplicable. In general,currentProject is used to indicatesomeone's current efforts (and implied interests, concerns etc.), whilepastProject 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. aDocument or to instances of the classProject, which might themselves have ahomepage. In practice, it seems to have been used in a similar way tointerest, referencing homepages of ongoing projects.

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Property: foaf:depiction

Thedepiction property is a relationship between a thing and anImage that depicts it. As such it is an inverse of thedepicts relationship.

A common use ofdepiction (anddepicts) 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 theregions 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.

Thedepiction property is a super-property of the more specific propertyimg, which is used more sparingly. You stand in adepiction relation toanyImage that depicts you, whereasimg is typically used to indicate a few images that are particularly representative.

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Property: foaf:depicts

Thedepicts property is a relationship between aImage and something that the image depicts. As such it is an inverse of thedepiction relationship. Seedepiction for further notes.

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Property: foaf:familyName

ThefamilyName property is provided (alongsidegivenName) for use when describing parts of people's names. Although theseconcepts 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 simplename property.

Support is also provided for the more archaic and culturally varying terminology offirstName andlastName.

See theissue tracker for design discussions, status and ongoing work on rationalising the FOAFnaming machinery.

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Property: foaf:firstName

ThefirstName property is provided (alongsidelastName) as a mechanism to support legacy data that cannot beeasily interpreted in terms of the (otherwise preferred)familyName andgivenName properties. The conceptsof 'first' and 'last' names do not work well across cultural and linguistic boundaries; however they are widely used in addressbooks and databases.

See theissue tracker for design discussions, status and ongoing work on rationalising the FOAFnaming machinery.

There is also a simplename property.

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Property: foaf:focus

Thefocus property relates a conceptualisation of something to the thing itself.Specifically, it is designed for use with W3C'sSKOS vocabulary, to help indicate specific individual things (typically people, places, artifacts) that are mentioned in different SKOS schemes (eg. thesauri).

W3C SKOS is based around collections of linked 'concepts', which indicate topics, subject areas and categories.In SKOS,properties of a skos:Concept are properties of the conceptualization (see2005 discussion for details); for example administrative and record-keeping metadata. Two schemes might have an entry for the same individual; the foaf:focus propertycan be used to indicate the thing in they world that they both focus on. Many SKOS concepts don't work this way; broad topical areas and subject categories don't typically correspond to some particular entity. However, in caseswhen they do, it is useful to link both subject-oriented and thing-oriented information via foaf:focus.

FOAF's focus property works alongside its other topic-oriented constructs:topic,primaryTopic are used when talking about the topical emphasis of a document. The notion ofprimaryTopic is particularly important in FOAF as it provides an indirect mechanism for identifying things indirectly. Asimilar approach is explored by theTDB URI scheme. FOAF includes topic-oriented functionality to address itsoriginal goals of linking people to information,as well as to other people, through the use of linked information.

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Property: foaf:gender

Thegender property relates aAgent (typically aPerson) 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 usegender in any particular document or description. Values other than 'male' and 'female' may be used, but are not enumerated here. Thegender mechanism is not intended to capture the full variety of biological, social and sexual concepts associated with the word 'gender'.

Anything that has agender property will be some kind ofAgent. However there are kinds ofAgent to which the concept of gender isn't applicable (eg. aGroup). FOAF does not currently include a class corresponding directly to "the type of thing that has a gender".At any point in time, aAgent has at most one value forgender. FOAF does not treatgender as astatic 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 allAgents (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 theirgender. 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, supportslying. 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 omitgender 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

ThegivenName property is provided (alongsidefamilyName) for use when describing parts of people's names. Although theseconcepts 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 simplename property.

Support is also provided for the more archaic and culturally varying terminology offirstName andlastName.

See theissue tracker for design discussions, status and ongoing work on rationalising the FOAFnaming machinery.

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Property: foaf:icqChatID

TheicqChatID property relates aAgent to a textual identifier assigned to them in the ICQ Chat system. See theicq 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 (seeaimChatID).

SeeOnlineChatAccount (andOnlineAccount) for amore general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:img

Theimg property relates aPerson to aImage that represents them. Unlike its super-propertydepiction, we only useimg 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 generaldepiction property (and its inverse,depicts), theimg property is only used with representations of people (ie. instances ofPerson). 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 thandepiction so we can have a useful way of picking out a reasonable image to represent someone. FOAF definesimg as a sub-property ofdepiction, which means that the latter relationship is implied whenever two things are related by the former.

Note thatimg does not have any restrictions on the dimensions, colour depth, format etc of theImage it references.

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

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Property: foaf:interest

Theinterest property represents an interest of aAgent, through indicating aDocument whosetopic(s) broadly characterises that interest.

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

Uses ofinterest 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 toCPAN)".

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'sinterest. 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:jabberID

ThejabberID property relates aAgent to a textual identifier assigned to them in theJabber messaging system. See theJabber 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 ofAgent (ie. things thatdo stuff). The uses of Jabber go beyond simple IM chat applications. ThejabberID property is provided as a basic hook to help support RDF description of Jabber users and services.

SeeOnlineChatAccount (andOnlineAccount) for amore general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:lastName

ThelastName property is provided (alongsidefirstName) as a mechanism to support legacy data that cannot beeasily interpreted in terms of the (otherwise preferred)familyName andgivenName 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 theissue tracker for design discussions, status and ongoing work on rationalising the FOAF naming machinery.

There is also a simplename property.

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Property: foaf:logo

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

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Property: foaf:mbox_sha1sum

Ambox_sha1sum of aPerson 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 ambox 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 ambox_sha1sum representation of it. Just as ambox can be used as an indirect identifier for its owner, we can do the same withmbox_sha1sum since there is only onePerson with any particular value for that property.

Many FOAF tools usembox_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 (seeEdd Dumbill's documentation) and the use ofFOAF-based whitelists for mail filtering.

Code examples for SHA1 in C#, Java, PHP, Perl and Python can be foundin Sam Ruby's weblog entry. Remember to include the 'mailto:' prefix, but no trailing whitespace, when computing ambox_sha1sum property.

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Property: foaf:msnChatID

ThemsnChatID property relates aAgent to a textual identifier assigned to them in the Microsoft online chat system originally known as 'MSN', and nowWindows Live Messenger.See theMicrosoft mesenger andWindows Live ID sites for more details.

SeeOnlineChatAccount (andOnlineAccount) for a more general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:myersBriggs

ThemyersBriggs 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. ThemyersBriggs property applies only to thePerson class; wherever you see it, you can infer it is being applied to a person.

ThemyersBriggs 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 ofweblog is an endorsement of soapboxes.

The values formyersBriggs 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 alsoCory 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

Thename 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 theissue tracker for status of work on this issue.

Thename property, like all RDF properties with a range of rdfs:Literal, may be used with XMLLiteral datatyped values (multiplenames 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

Thenick property relates aPerson 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 andicqChatID. 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. TheOnlineAccount term (and supporting vocabulary) are provided as a more verbose and more expressive generalisation of these properties.

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Property: foaf:openid

Aopenid is a property of aAgent that associates it with a document that can be used as anindirect identifier in the manner of theOpenID "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.

Theopenid property is "inverse functional", meaning that anything that is the foaf:openid of something, is theopenid 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 andGroup, that allow for such scenarios to be consistent with the notion that any foaf:openid is the foaf:openid of just oneAgent.

FOAF does not mandate any particular URI scheme for use asopenid values. The OpenID 1.1 specification includes adelegation 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 similartechnique 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:pastProject

After aPerson is no longer involved with acurrentProject, or has been inactive for some time, apastProject relationship can be used. This indicates thatthePerson was involved with the described project at onepoint.

If thePerson 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.), whilepastProject describes what they've previously been doing.

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Property: foaf:phone

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

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Property: foaf:plan

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

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

SeeHistory of the Finger Protocol by Rajiv Shah for more on this piece of Internet history. Thegeekcode property may also be of interest.

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Property: foaf:publications

Thepublications property indicates aDocumentlisting (primarily in human-readable form) some publications associated with thePerson. Such documents are typically published alongside one'shomepage.

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Property: foaf:schoolHomepage

TheschoolHomepage property relates aPerson to aDocument that is thehomepage 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 ofOrganization). The original application area forschoolHomepage 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 usingschoolHomepage.

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 studiedhere' 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:skypeID

Theskype property relates aAgent to an account name of a Skype account of theirs.

SeeOnlineChatAccount (andOnlineAccount) for amore general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:thumbnail

Thethumbnail property is a relationship between a full-sizeImage and a smaller, representativeImage that has been derrived from it.

It is typical in FOAF to expressimg anddepiction relationships in terms of the larger, 'main' (in some sense) image, rather than its thumbnail(s). Athumbnail 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 thumbnaildepicts 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.

Athumbnail is typically small enough that it can beloaded and viewed quickly before a viewer decides to download the largerversion. They are often used in online photo gallery applications.

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Property: foaf:tipjar

Thetipjar property relates anAgentto aDocument that describes some mechanisms forpaying or otherwise rewarding that agent.

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

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

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Property: foaf:title

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

The approriate values fortitle 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:topic

Thetopic property relates a document to a thing that the document is about.

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

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Property: foaf:topic_interest

Thetopic_interest property links aAgent to a thing that they're interested in. Unliketopic it is not indirected through a document, but links the thing directly.

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Property: foaf:workInfoHomepage

TheworkInfoHomepage of aPerson is aDocument that describes their work. It is generally (but not necessarily) a different document from theirhomepage, and from anyworkplaceHomepage(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

TheworkplaceHomepage of aPerson is aDocument that is thehomepage of aOrganization 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 aPerson and anOrganization that they work for.

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Property: foaf:yahooChatID

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

SeeOnlineChatAccount (andOnlineAccount) for amore general (and verbose) mechanism for describing IM and chat accounts.

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Property: foaf:age

Theage property is a relationship between aAgent and an integer string representing their age in years. See alsobirthday.

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Property: foaf:birthday

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

See alsoage.

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Property: foaf:membershipClass

ThemembershipClass property relates aGroup to an RDF class representing a sub-class ofAgent whose instances are all the agents that are amember of theGroup.

SeeGroup for details and examples.

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Property: foaf:sha1

Thesha1 property relates aDocument to the textual form of a SHA1 hash of (some representation of) its contents.

The design for this property is neither complete nor coherent. TheDocument class is currently used in a way that allows multiple instances at different URIs to have the 'same' contents (and hence hash). Ifsha1 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:status

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

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Property: foaf:dnaChecksum

ThednaChecksum 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:family_name

This property is considered anarchaic spelling offamilyName.

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Property: foaf:fundedBy

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

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

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Property: foaf:geekcode

Thegeekcode property is used to represent a 'Geek Code' for somePerson.

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

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Property: foaf:givenname

ThegivenName property is provided (alongsidefamilyName) for use when describing parts of people's names. Although theseconcepts 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 simplename property.

Support is also provided for the more archaic and culturally varying terminology offirstName andlastName.

See theissue tracker for design discussions, status and ongoing work on rationalising the FOAFnaming machinery.

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Property: foaf:holdsAccount

This property is consideredarchaic usage. It is generally better to useaccount instead.

TheholdsAccount property relates aAgent to anOnlineAccount for which they are the sole account holder. SeeOnlineAccount for usage details.

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

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Property: foaf:surname

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

There is also a simplename property.

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Property: foaf:theme

This property is consideredarchaic usage, and is not currently recommended for usage.

Thetheme 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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