W3C home > Mailing lists > Public > public-rdf-in-xhtml-tf@w3.org > December 2007

Re: CURIE syntax thoughts + @instanceof semantics

From: Mark Birbeck <mark.birbeck@x-port.net>
Date: Mon, 17 Dec 2007 12:12:01 +0000
Message-ID: <a707f8300712170412s2715ad36t77f4ceffc4f23a65@mail.gmail.com>
To: "Ivan Herman" <ivan@w3.org>
Cc: "W3C RDFa task force" <public-rdf-in-xhtml-tf@w3.org>

Hi Ivan,

> Well... We already add some extra semantics (including in the pure CURIE
> syntax) to "_:a"; we talk about globally unique value, which is
> something special (let alone in RDFa term).

The whole point of my post was to explain that we actually *don't* do
anything special in RDFa with respect for CURIEs. :) Thanks for
bringing this out though, because I realise now that the CURIE draft
is not up-to-date in this regard.

As we know, CURIEs deals in mappings from one string to another. One
way of creating a mapping is by using @xmlns, but there are other
ways, and in fact, the CURIE spec is agnostic about how you get your

All the CURIE spec does is to say that if you have a mapping for
"foaf", then the following CURIE:


would become a URI that is the concatenation of the value in the map
for "foaf", and the URI "name".

Now, bnodes are actually nothing special in the world of URIs. All
they are is identifiers that are internally consistent, but not
available globally. So if a CURIE processor were to initialise it's
mapping tables with an entry for "_" which maps to
"bnode:url-of-the-document#", or any other algorithm you can think of
to get a unique identifier, then all is well. Then the CURIE:


will map to:


This means, by the way, that CURIEs will 'just work' in other
languages such as SPARQL.

(I'm aware that the set of bnodes is supposed to be disjoint with the
set of URIs, but since a URI can be just about anything, this is nigh
on impossible to achieve in practice. So the next best thing is to
devise a class of URIs that are so unlikely to ever occur in real life
as to be for all intents and purpose, disjoint from the set of URIs.)

> So I do not think why we
> would not agree to add some special semantics to "_:" (at least in
> RFDa).

Because, firstly, the idea of unique identifiers in CURIEs is not
unique to RDFa, and secondly, there are no special semantics for

> It does sound like a good idea, it fills a 'hole' in usage...

I agree with you there. It's just that, as I tried to say before, the
syntax you are proposing already means something and is consistent.
It's not 'available', I'm afraid.

> Regardless of the @instanceof: at the moment, if we use "_:a" to
> generate a BNode, that portion of the code, as we all know, is not
> necessarily copy-pastable.

Yes, I agree. It's exactly the same problem with @id in XML. But we
may not be able to fix this, in this version of RDFa, although I would
hope that nothing we do now will prevent us from fixing it in the

> With the usage of "_:' it is.

With the usage of some appropriate syntax, it is. ;) Not this one, though.



  Mark Birbeck, formsPlayer

  mark.birbeck@formsPlayer.com | +44 (0) 20 7689 9232
  http://www.formsPlayer.com | http://internet-apps.blogspot.com

  standards. innovation.
Received on Monday, 17 December 2007 12:12:19 UTC

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