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Re: RDFa Lite and non-RDFa @rel values

From: Gregg Kellogg <gregg@greggkellogg.net>
Date: Wed, 25 Apr 2012 12:23:03 -0400
To: Alex Milowski <alex@milowski.com>
CC: RDFa WG <public-rdfa-wg@w3.org>
Message-ID: <C60491A9-0F8A-4A9B-996B-907BDBF159B3@greggkellogg.net>
On Apr 25, 2012, at 8:04 AM, Alex Milowski wrote:

> On Wed, Apr 25, 2012 at 7:43 AM, Ivan Herman <ivan@w3.org> wrote:
> 
>>>> Well, in my view, none of the two. I believe the response should be:
>>>> 
>>>> <> <...homepage> <http://www.w3.org/> .
>>>> 
>>>> And nothing else.
>>> 
>>> In HTML5 with the HTML or XHTML syntax?
>> 
>> Both HTML5 and XHTML5.
> 
> Looking at the rules in both the HTML+RDFa and XHTML+RDFa documents, I
> think any HTML5 document serialized as XHTML will be served as
> "application/xhtml+xml" and so the the "XHTML+RDFa 1.1" initial
> context will be used.  As such, they'll be different.

No, there are specific tests for XHTML5 vs XHTML1, and processors are expected to tell the difference between the two. Looking at test case 0176, for example, we have the following documents [1] [2]:

XHTML5:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:foaf="http://xmlns.com/foaf/0.1/">
...
</html>

XHTML1:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.1//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-2.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" version="XHTML+RDFa 1.1" xmlns:foaf="http://xmlns.com/foaf/0.1/">
...
</html>

The content-type is only one such mechanism, which is shared between XHTML1 and XHTML5. 

Note the difference in DOCTYPE. Also, in this case, the XHTML1 contains an @version attribute, which is obsoleted in (X)HTML5.

According to XHTML+RDFa 1.1 document conformance [3], there are MAY statements for @version and the DTD. This is sufficient to tell an XHTML1+RDFa document from an XHTML5+RDFa document, which would contain a different DTD. Of course, if it is ambiguous, a processor can pick either, however it can be made unambiguous, so that there is a mechanism for distinguishing the processing rules, which the test suite uses to test different behavior.

Gregg

[1] http://rdfa.info/test-suite/test-cases/rdfa1.1/xhtml5/0176.xhtml
[2] http://rdfa.info/test-suite/test-cases/rdfa1.1/xhtml1/0176.xhtml
[3] http://www.w3.org/TR/2012/CR-xhtml-rdfa-20120313/#document-conformance

>> 
>> I think the sentiment in the group, and definitely the feedbacks we got from different users, was that the automatic usage of the XHTML1 @rel value was not very popular (a typical case of pollute the space with triples originating from rel="stylesheet"). (At least that is my impression.) The only reason we kept the XHTML1 version was backward compatibility...
>> 
> 
> Your pollution is my useful information.  Specifically, I really want
> @rel="related" and @rel="alternate" but there are other useful values.
> Of the values, only "noreferrer", "prefetch", and "stylesheet" have
> operational (e.g. browser rendering, operation, etc.) semantics.  Even
> "nofollow", which is strangely named, has useful semantics: "Indicates
> that the current document's original author or publisher does not
> endorse the referenced document."
> 
> If we didn't want "stylesheet" and few others, why didn't we just
> leave them out of the initial context?
> 
>> 
>> With my W3C hat on:-) the extra processing on removing @rel values is defined for HTML5 only. It does not change the core processing steps. HTML5+RDFa language profile is defined as a recommendation by the HTML5 WG, and that is still further down the line. So we do not have a process issue for this.
>> 
> 
> So, we'd change the HTML5+RDFa document to modify the sequence
> algorithm by reference?
> 
> If so, doesn't that mean we'd make XHTML and HTML syntaxes have even
> more different outcomes?  That is, assuming use of the XHTML+RDFa
> profile for XHTML syntax HTML5 documents.
> 
> Obviously, this is a "hot button" issue for me.  I doubt I'm alone but
> I understand there are many other users out there.
> 
> -- 
> --Alex Milowski
> "The excellence of grammar as a guide is proportional to the paucity of the
> inflexions, i.e. to the degree of analysis effected by the language
> considered."
> 
> Bertrand Russell in a footnote of Principles of Mathematics
> 
Received on Wednesday, 25 April 2012 16:28:54 GMT

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