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Re: Consensus on alternate prefixing mechanism

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Thu, 30 Apr 2009 00:18:48 -0400
Message-ID: <49F926A8.4080406@digitalbazaar.com>
To: RDFa Developers <public-rdf-in-xhtml-tf@w3.org>
Ivan Herman wrote:
> - Is the following acceptable: @prefix="=http://a.b.c/" ?
> 	my option would be yes, and it sets the default namespace.
> 	It could be equivalent to a xmlns="http://a.b.c/"

Most of this discussion about changing the default namespace has
happened offline over the past couple of months. During the telecons, we
didn't discuss in detail or form a consensus on how one would override
the default namespace.

The other option that has been floated over the past couple of months
was using a reserved word, so something like:

@prefix="DEFAULTNS=http://a.b.c/"

We could discuss further if a number of people felt that we needed a
mechanism to override the default namespace. It seems like we really
should define such a mechanism.

Personally, I'd prefer a reserved word mechanism over the other method
because:
   * It would probably be easier for non-developers to understand.
   * It would be harder to mistakenly override the default namespace.
   * It would be easier for the parser writers to handle.

> - Is the following acceptable: @prefix="aa="
> 	my option would be no, this is an error, and the RDFa
> 	processor should simply ignore that

I believe that the current regex would not match "aa=" and would thus
ignore it. However, if one were to do prefix="aa= bb=http://foo.com",
that may cause an issue. We should really have a couple of approved test
cases for these error conditions in the Design Suite. I'll try and take
an action to create some valid Design Suite test cases for @prefix.

> - What happens if there is, on an element, both an xmlns and a prefix?
> Ie, if I have
> 
> <bla xmlns:aa="http://www.w1.com/" prefix="aa=http://www.w2.com/"/>
> 
> what is the URI corresponding to the "aa" prefix? I know there were
> discussions on the task force, but it is not documented on the wiki...

There are currently mixed feelings on this. At first, we believed that
xmlns and prefix would exist in the same language, but now there are
concerns that this may confuse people (having two ways to do the same
thing). This issue can be worked through, so let's assume that prefix
and xmlns can be defined in the same document.

I believe that the current consensus is that you would process both
lists, but one would take precedence over the other. So, for example, if
@xmlns took precedence over @prefix, you would process @prefix first and
then @xmlns. Any conflicting mappings would be overwritten when @xmlns
is processed. The last defined value wins.

I have noted these issues on the rdfa.info wiki:

http://rdfa.info/wiki/alternate-prefix-declaration-mechanism#Outstanding_Issues

Anybody else disagree or have more input on these issues?

-- manu

-- 
Manu Sporny
President/CEO - Digital Bazaar, Inc.
blog: A Collaborative Distribution Model for Music
http://blog.digitalbazaar.com/2009/04/04/collaborative-music-model/
Received on Thursday, 30 April 2009 04:19:26 GMT

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