The external FOAF URL can be set on your Personal Information page, at http://www.livejournal.com/editinfo.bml . Under advanced options, there is a field labeled "External FOAF URL". This URL will let LiveJournal know that you already have a FOAF file created elsewhere on the net, and that you would prefer that people be redirected to this URL.
The following is an example FOAF file created when you set "External FOAF URL".
<?xml version='1.0'?> <rdf:RDF xml:lang="en" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:foaf="http://xmlns.com/foaf/0.1/" xmlns:dc="http://purl.org/dc/elements/1.1/"> <foaf:Person> <foaf:nick>crschmidt</foaf:nick> <foaf:dateOfBirth>1984-04-19</foaf:dateOfBirth> <foaf:mbox_sha1sum>bbff51a6d70630daafe242c186a6e27fda3e99c7</foaf:mbox_sha1sum> <foaf:page> <foaf:Document rdf:about="http://www.livejournal.com/userinfo.bml?user=crschmidt"> <dc:title>LiveJournal.com Profile</dc:title> <dc:description>Full LiveJournal profile, including information such as interests and bio.</dc:description> </foaf:Document> </foaf:page> <rdfs:seeAlso rdf:resource="http://www.crschmidt.net/foaf.rdf"> </foaf:Person> </rdf:RDF>
As you can see, no information such as foaf:knows fields is included in this file: these fields are excluded when the seeAlso field is included. If you plan to spider the information presented by LiveJournal, you should ignore all other information presented in this FOAF file - although it may or may not be accurate, it is not the canoncial source of information for the user. They set the External FOAF URL specifically so that this information can be presented in a different location.
In summary: External FOAF set on editinfo. Replaces all your FOAF:interests, foaf:knows, etc. with a bare bones document containing very little information. Any other information in this type of feed should be ignored. Check for a seeAlso before you store information from a feed. Example feed stored above.