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[URGENT] Re: RDFa Core 1.1 XML+RDFa spec bug?

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Thu, 24 Mar 2011 22:21:16 -0400
Message-ID: <4D8BFC1C.8000702@digitalbazaar.com>
To: RDFa WG <public-rdfa-wg@w3.org>
On 03/24/2011 10:39 AM, Shane McCarron wrote:
> I disagree - we say this EXPLICITLY already.  For all contexts. 
> ...
> Note that the parent subject is set to the base value.  What am I
> missing here?

That 'parent subject' has nothing to do with setting the 'new subject'
when operating on the root element of the document. However, the 'new
subject' is eventually initialized to the 'parent subject' when step #13
is hit when processing all elements nested under the root element.

We have a problem - and I've verified that problem with Shane, Mark, and
Gregg. This is a non-editorial problem, and is a bug with RDFa 1.0. We
didn't see the issue until now because the XHTML+RDFa spec masked the
problem by setting about="" on HEAD and BODY.

However, XML+RDFa 1.1 doesn't do this, but the processing rules will
eventually set the 'new subject' to the value of 'base' via this rule in
step #13:

http://www.w3.org/2010/02/rdfa/sources/rdfa-core/#PS-recurse

Specifically, this is run for the root element:

"""
* the base is set to the URI of the document (or another value
  specified in a language specific manner such as the HTML base
  element);
* the parent subject is set to the base value;
"""

and then this

"""
the parent object is set to value of current object resource, if
non-null, or the value of new subject, if non-null, or the value of the
parent subject of the current evaluation context;
"""

then this is run for the element under the root element:

"""
new subject is set to the URI obtained from the first match from the
following rules:
...
otherwise, if parent object is present, new subject is set to the value
of parent object. Additionally, if @property is not present then the
skip element flag is set to 'true';
"""

That makes the resolution we made today absolutely wrong:

http://www.w3.org/2010/02/rdfa/meetings/2011-03-24#resolution_2

It also means that we have had a bug for SVGTiny1.2+RDFa 1.0 for quite
some time (but it really didn't affect anybody).

We need to fix this before 2nd Last Call because it could result in a
3rd Last Call. We /could/ go into 2nd Last Call and say that we're not
going to address this issue, but it will inevitably lead to someone
asking why this:

<svg property="dc:title" content="The Image">...</svg>

doesn't result in a triple, but this does:

<svg><g property="dc:title" content="The Image">...</g></svg>

and why this results in a blank-node of type "foaf:Document":

<svg typeof="foaf:Document">...</svg>

The current approach to fix this is to assume about="" on the root
element of all RDFa documents. This works across HTML, XML, SVG and all
other document types. We already explored initializing 'new subject' to
'base', and 'parent object' to 'base' - they're both problematic.
Shane's having a think on it.

Here's what we'll try to do tomorrow:

1. PROPOSE and RESOLVE to fix the issue above, retracting the decision
   made today about XML+RDFa and about="" (which is clearly wrong).
2. PROPOSE and RESOLVE to go into 2nd Last Call with the change made
   in #1.

We will be PROPOSE/RESOLVING via this mailing list, so it is vital that
as many RDFa WG members respond with their "+1/-1" as possible. So, keep
your eyes peeled for the proposals tomorrow and make sure to send in
your +1/-1 or we'll miss our narrow window for 2nd LC.

-- manu

-- 
Manu Sporny (skype: msporny, twitter: manusporny)
President/CEO - Digital Bazaar, Inc.
blog: Payment Standards and Competition
http://digitalbazaar.com/2011/02/28/payment-standards/
Received on Friday, 25 March 2011 02:22:02 UTC

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