Adding extra fields to a FOAF file

I would like to store my personal data in a FOAF file on my own server. There is a group of us doing the same thing. We need a couple of custom fields that the standard FOAF implementation doesn't have, ie: availability.

How can I add the availability field, and still keep the FOAF file validated? I guess I use the RDF format outside of the FOAF block, but I am not quite sure how to do that 'legally'. Here is a sample of FOAF code.

<?xml version="1.0"?>

    <rdf:RDF xmlns:rdf="http://www.w3开发者_如何学编程.org/1999/02/22-rdf-syntax-ns#"
             xmlns:foaf="http://xmlns.com/foaf/0.1/">
      <foaf:Person>
       <foaf:name>Joe Blogs</foaf:name>
       <foaf:gender>Male</foaf:gender>
       <foaf:title>Mr</foaf:title>
       <foaf:givenname>Joe</foaf:givenname>
       <foaf:family_name>Blogs</foaf:family_name>
     </foaf:Person>
    </rdf:RDF>

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It's really simple, you just need an 'availability' property. You could just make up a namespace and use it:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:foaf="http://xmlns.com/foaf/0.1/"
         xmlns:myvocab="http://my.example.org/vocab#">
   <foaf:Person>
     <myvocab:availability>....</myvocab:availability>
     <foaf:name>Joe Blogs</foaf:name>
     ....
   </foaf:Person>
</rdf:RDF>

Perfectly legal. Ideally you would host an rdf file describing the property at http://my.example.org/vocab, so people could look up the property.

However even easier is open.vocab.org. There you can define you little property and it will be retrievable. The namespace will be http://open.vocab.org/terms/, and the property name will be, well, whatever you pick.

(It may be that there's a relevant property out there already, of course. Try asking on the foaf list)

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Yes, FOAF was designed (by using RDF) to allow just this kind of casual extensibility. You can add anything you like so long as it parses as RDF (see http://www.w3.org/RDF/Validator )