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Re: Validating XHTML with embedded RDF

From: Joseph Reagle <reagle@w3.org>
Date: Wed, 25 Jun 2003 17:46:40 -0400
To: Dan Brickley <danbri@w3.org>
Cc: Masayasu Ishikawa <mimasa@w3.org>, public-rdf-in-xhtml-tf@w3.org
Message-Id: <200306251746.41014.reagle@w3.org>

On Wednesday 25 June 2003 16:41, Dan Brickley wrote:
> My understanding that we already have a generic metadata syntax, ie.
> RDF/XML; I'm hoping we'll find a way to allow XHTML 2.0 documents to be
> enthusiatically deployed with embedded islands of full RDF/XML (eg. in a
> <meta/> element or elsewhere), rather than have to wait for XHTML 3.0.

hrmm... Let me see if I can successfully pull together a map of the 
landscape as I see it now:

XHTML1.*
1. Hacks: 
 a. Commenting out the RDF, 
 b. Sticking in a script tag.

Assessment: These are architecturally inelegant -- though I actually prefer 
the script element over comments and wonder what led CC to use a comment... 
These are the solutions to beat.

2. Validation: 
 a. Create a version of a simple RDF syntax (for relatively "flat" data) 
that could be squeezed into the meta elements in some way. This is what 
many of the scenarios seem to require, but folks also say they want 
arbitrary RDF.
 b. Create a version of a general  RDF syntax that is validatable by a DTD. 
The RDF community doesn't seem to want create a new or constrained syntax.
 c. Create a new sort of XHTML1.* document using XML Schema where the XHTML 
is strictly validated, and the RDF/XML is laxly validated. Mimasa has 
written such a schema.
d. Create a new sort of XHTML1.* document using NRL, Schema, and RNG where 
the XHTML is strictly validate by Schema, and the RDF/XML is validated 
using RNG. Mimasa has written such a schema.
e. Create a new sort of XHTML1.* document using RNG that validates the XHTML 
and RNG. This is the only thing *not* done by Mimasa <smile/>, though I 
assume it could be done?

Assessment: Since Schema is mature and a W3C REC, I think option C has the 
most likely chance of success and it requires constituencies to write the 
formal specification, the schemas, and support a validator. The schemas are 
already written, and I think a validator could be trivially layered on top 
of XSV, so the task would then to formally specify it and publish it as a 
NOTE, RFC, or REC...

3. Semantics:
a. Solve the arbitrary semantics of mixed XML problem.
Assessment: I'm avoiding the issue the TAG is facing on what is the 
"meaning" of all these things when combined beyond "ignore the namespaces 
you don't know."
  http://www.w3.org/2002/04/htmlrdf

4. **Conclusion**: Dan (and others), do you support my proposal to create a 
XHTML(valid)+RDF(lax) document for XHTML 1.*?
  http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2003Jun/0012



XHML2.0
Similar to XHTML1.* but we know:
1. It will be based on XML Schema from the start -- though I'm still unsure 
what that community will do without the entities they are so fond of.
2. They will have a richer, nested, metadata element which could be 
exploited *if* folks were receptive to re-casting RDF into a meta-data tag; 
but they don't seem to be, see 2a above. 
3. They have *NOT* agreed to replace the meta element with RDF, nor to use 
it nor lend it any support beyond possibility of ignoring it (i.e., laxly 
valid). This is because even XML Schema can't validate generic RDF. I think 
to get the HTML WG to actually include and *rely* upon RDF as part of the 
core specification, I think they'd have to use RNG, which I don't think is 
likely. (Again, we could define a document on the side and provide a 
validator, but it wouldn't be *part* of the core XHTML spec.)
Received on Wednesday, 25 June 2003 17:46:45 GMT

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