I have an action from the Vocabulary Management task force of the W3C SW Best Practices Working Group to document the way the FOAF namespace currently works. Here goes.
The FOAF RDF vocabulary is named by the URI http://xmlns.com/foaf/0.1/ and has information available at that URI in both machine-friendly and human-friendly form. When that URI is dereferenced by HTTP, the default representation is currently HTML-based.
Aside: I say based because the markup, while basically being XHTML, also includes incline RDF/XML describing the FOAF vocabulary. The HTML TF of SWBPD WG is looking at ways of making such documents validatable; I hope a future version will be valid in some way, as well as presentable in mainstream browsers. This might be via RDF/A in XHTML2, RDF/A back-ported to an early XHTML variant, a GRDDL-based transform, or perhaps a CDF document if they’re deployable in legacy browsers.
Backing up to the big picture: we want to make it easy for both people and machines to find out what they need. So the basic idea is that there’s an HTML document describing FOAF for humans, and a set of RDF statements describing FOAF for machines. The RDF statements are available in several ways. As embedded RDF/XML in the HTML page. As a separate index.rdf document (this should be LINK REL’d from the former), and as a content-negotiable representation of the main URI, available to clients that send an “Accept: application/rdf+xml” header.
In addition to this, each FOAF term (assuming the Apache .htaccess is up to date; this might not be currently true) is redirected by the Web server to the main FOAF namespace URI. For example, http://xmlns.com/foaf/0.1/Person. This should in the future be done with a 303 HTTP redirection code, to be consistent with the recent W3C TAG decision on http-range-14 (apologies for the jargon and lack of links to explanation). Because FOAF term URIs don’t contain a # [edit: I wrote / previously; thanks mortenf], note that the redirection can’t point down into a sub-section of the HTML document. To make the HTML document more usable, we should probably put a better table of contents for terms nearer to the top of the page, to allow someone to navigate quickly to the description of that term.
One last point: each term defined in FOAF is accompanied not only by a label and comment (standard from RDFS); it also has a chunk of HTML markup, with cross-references to other terms. At the moment, this is not made available in any machine-readable form. There might be some scope here for common practice with SKOS and other vocabularies?
Sorry for the hasty writeup, I just wanted to get this recorded as a starting point…