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Re: metadata content

From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>
Date: Wed, 19 Nov 2008 12:25:13 +0200
To: public-html@w3.org
Message-Id: <200811191125.14197.Dr.O.Hoffmann@gmx.de>

> On Tue, 18 Nov 2008, Dr. Olaf Hoffmann wrote:
> > I would only like to know, if I interprete this correct, that authors
> > finally can put metadata elements from other namespaces like RDF in the
> > head element of a HTML5 document without any conflicts?

Ian Hickson:
> In the XML serialisation, yes.


Ok, XML formats provide anyway much more possibilities for authors
than HTML4 or HTML5. For XML it is not really a problem anyway, because
in doubt one can always use a compound document with a root-element 
from a language with sufficient capabilities.
To avoid disappointments, it might be a good idea to say something 
like:
"In the XML serialisation elements from other namespaces whose semantics 
are primarily metadata-related (e.g. RDF) are also metadata 
content."

The case for the HTML5 variant looks more problematic, because
currently the profile attribute is removed too, which had the
capability to produce something like a defined 
subject-predicate-object construction together with meta elements.
Well, from a current point of view, the HTML4 profile strategy is
not thought through anyway, but for simple applications still sufficient.
The profile attribute seems to be used for example by DCMI, or 
'microformats' uses it to map class value items to specific meanings.
What seems to be left for HTML5 is the a/link with rel="profile".
However, because there is no useful substructure for metadata
in the HTML:head, it is not possible to map a link to only a group
of meta elements, all this looks pretty plurivalent already in HTML4.
(Currently I consider some similar approaches for a collection of 
roles with a semantical meaning, mainly intended for a use with the
XHTML:role or SVGT1.2:role attribute not present currently in HTML5,
to map them to class value items to be usable too in HTML4, 
XHTML1.0/1.1 and HTML5).
The main problem of these possible HTML4 or HTML5 constructions
I can see is, that it is difficult (or impossible) to address a specific
element with metadata content as with 'about' from RDF for example.
The other problem is, that it is difficult (or impossible) to use more
than one resource for the definition of metadata and there are
several, not just DCMI or microformats or my 'collection'.
Therefore some advanced metadata strategy like RDF or the
RDFa approach could be very helpful for authors, even if they
do not use already the XML serialisation, but still the 'HTML5
serialisation'.
Will RDFa be adopted into HTML5? What about XHTML:role including
CURIEs? (The CURIEs are a quite important feature, because
the current role draft does not have predefined values for
many applications and will never have for any application. 
This requires the namespaces to link somehow to the definition 
of the meaning of roles and metadata.)
Is there any idea for a convenient use of structured metadata
in HTML5?
Is there any idea to structure metadata with HTML5 elements
or to adopt some RDF approach to avoid to reinvent the wheel?


....

Ian Hickson:
> > Assuming the validator is aware of the vocabulary, then it should work
> > fine. (That is, XHTML5+RDF should work fine in a validator that
> > supports
> > XHTML and RDF. If the validator doesn't support RDF, it won't work.)
>

Henri Sivonen:
> Validator.nu does a third thing: It doesn't support RDF (it doesn't
> contain an RDF validator) but it doesn't treat it as an error, either.
> It warns that it can't check RDF and uses a wildcard content model for
> {http://www.w3.org/1999/02/22-rdf-syntax-ns#}RDF.

Yes, this sounds like a much more meaningful approach for elements
from unkown namespaces than I know from other validators ;o)


Olaf
Received on Wednesday, 19 November 2008 10:28:56 GMT

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