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Re: CURIEs: A proposal

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Fri, 09 Jun 2006 10:36:41 +0100
Message-ID: <44894129.6080002@ibiblio.org>
To: mark.birbeck@x-port.net
Cc: www-tag@w3.org, public-rdf-in-xhtml-tf@w3.org

I think Henry's pointing to the conceptual problem with making CURIEs a
"superset" of QNames.  Unlike CURIEs, QNames (at least as I've been able
to discover, correct me if I'm wrong - the spec just seems silent) do
not define an algorithm for converting an entire QName to a IRI, and by
"algorithm" we're not talking about anything fancy - but just
concatenating the namespace URI and the local name as strings, which is
what most processors do anyways - as pointed out by Borden [1] and
raised to the TAG [2], who seemed to be answer a sort of different
question in their finding.

Yet a processor can map (expanded name, local name)  like
(http://www.w3.org/1999/XSL/Transform,template) to an IRI by doing:


Or by doing:


And it seems both would be equally valid or invalid, depending on your

So by making CURIEs a superset of QNames is a bit difficult as long as
the QName (namespace prefix, local name)=>IRI construction is
unspecified. And so using the ":" for QNames and CURIEs means that given
any "x:y" element or attribute name one couldn't tell whether one meant
an IRI or a (namespace prefix, local name). So there seems to be two

1) Unspecified IRI construction for the entire (namespace prefix, local
name) a *bug* in QNames and should be corrected post-hoc by the CURIE
proposal. If this is the case, then CURIEs should use ":" and then make
themselves a superset of QNames.


2) Unspecified IRI construction in QNames is a *feature*  and so CURIEs
exist as a parallel standard, and so use [insert character besides ":"
here] in order to keep confusion between QNames and CURIEs at a minimum.

 My earlier post is that some communities (i.e. some of the microformat
people I talked to at WWW2006) mentioned that they would like another
character besides : for "namespaces in microformats." Next time I'll
just tell them to escape their colons :)

[1] http://www.openhealth.org/RDF/QNameQuagmire.html
[2] http://www.w3.org/2001/tag/issues.html#rdfmsQnameUriMapping-6

Mark Birbeck wrote:
> HI Henry,
>> My initial reaction is similar to Stuart's -- there's a lot to agree
>> with here, but
>>  1) I think we do better to keep QNames (shorthand for an *expanded
>>     name* which is a pair of an absolute IRI and an NMTOKEN local
>>     name) and CURIEs (shorthand for an IRI) clearly distinguished
>>     conceptually;
> Great...I've constantly tried to emphasise that my first motivation is
> to 'unpollute' QNames. The syntax is secondary--it's the fact that
> QNames represent XML elements and attributes, and yet have been used
> in numerous places as a shorthand for URIs, that I object to.
> (I'm not the first to have objected, of course! People involved in
> early RDF work were also aware that using QNames for predicates was
> dodgy, but they reluctantly went ahead in the absence of an
> alternative.)
>>  2) We think seriously about an alternative to the ':' as the
>>     separator for CURIEs.
> Firstly, I think that horse has bolted. The ':' is used in all sorts
> of places to indicate scoping, not just QNames, precisely because it
> feels so natural. It's used in URN values, in IPTC subject codes, and
> so on.
> Secondly, and more importantly, I'm proposing that many current uses
> of QNames should actually be CURIEs, and we therefore need to ensure
> backwards compatibiliy. For example, in your own work, Henry, XML
> Schemas should not be using QNames to identify datatypes for use in
> other langauges, or to name simple and complex types in schema
> definitions. Equally, XPath functions should not be declared using
> QNames.
> ...I could go on. :)
> So for backwards-compatibility reasons, I think it is a good thing if
> documents don't need to be changed.
> Regards,
> Mark
> Mark Birbeck
> x-port.net Ltd.
> e: Mark.Birbeck@x-port.net
> t: +44 (0) 20 7689 9232
> w: http://www.formsPlayer.com/
> b: http://internet-apps.blogspot.com/
> Download our XForms processor from
> http://www.formsPlayer.com/


Harry Halpin,  University of Edinburgh 
http://www.ibiblio.org/hhalpin 6B522426
Received on Friday, 9 June 2006 14:35:55 UTC

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