foaf:focus property relates a conceptualisation of something to the thing itself.
Specifically, it is designed for use with W3C's SKOS
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 (see 2005 discussion for details); for example administrative and record-keeping metadata. Two schemes might have an entry for the same individual; the foaf:focus property can 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 cases when 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:
are used when talking about the topical emphasis of a document. The notion of
is particularly important in FOAF as it provides an indirect mechanism for identifying things indirectly. A
similar approach is explored by the TDB URI scheme. FOAF includes topic-oriented
functionality to address its original goals of linking people to information,
as well as to other people, through the use of linked information.