Thanks Eric.

Let me explain my problem a bit better. I'm interested in alternative money systems, and I'd like to add a "currency" extension to the FOAF person tag so that a person can describe which economic networks they're members of.

Now in my naive XML I'd write something like this (let's use AM as the namespace of my currency tags)

<foaf:person rdf:id="foo">
<AM:currency rdf:id="mydollar">
<AM:name>MyDollar</AM:name>
<AM:paynet url="paymentEnabler.com" />
<AM:mutualCredit />
<AM:demurrage />
%lt;/AM:currency>

etc.

where the demurrge and mutualCredit tags represent boolean flags. Either the currency has these properties or doesn't.

But I don't know if this is allowed. I suppose I could also write :

<AM:demurrage>True</AM:demurrage>

Which raises the question, if "demurrage" isn't true, do I also need to explicitly represent

<:AM:demurrage>False</AM:demurrage>

It seems this might be something which is free for my application to decide, that I can allow the absence of the tag to imply false. Or it might be something where RDF has an implicit interpretation eg. when a tag is missing it means "undefined". So I shouldn't be using it to imply false.

Any intuitions on this?

Cheers

phil