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Re: My action item on RDDL/RDF

From: Paul Prescod <paul@prescod.net>
Date: Sun, 10 Nov 2002 15:31:29 -0800
Message-ID: <3DCEEC51.4050600@prescod.net>
To: Tim Bray <tbray@textuality.com>, WWW-Tag <www-tag@w3.org>

Tim Bray wrote:
> 
> ...
> 
> Now the 2nd RDF assertions in the two RDDLs are in conflict.  The reason 
> is that they involve 2 different namespaces, but the namespace doesn't 
> get into the RDDL.  But it could, be cause we know the URI of the 
> namespace ("" - this is the namespace doc remember) so we can make 
> assertions about it.

I would strongly encourage you to make it at LEAST a SHOULD that RDDL 
documents say explicitly what the namespace is. RDDL documents will and 
should get cached offline. There will be issues of trailing slashes that 
appear and disappear depending on the web server configuration. There 
will be case sensitivity issues. Some purists will add pound signs to 
namespace names and these may be (should be?) stripped in the 
interpretation of the relative URI.

If I use the wrong URI to register a RDDL with the semantic web or XML 
web equivalent of Google, there should be enough information built-in 
for it to recover.

And what about XSLT and CSS stylesheets (and in fact almost any other 
processor) which are just handed the document and told to do something 
useful with it. You're increasing the coordination costs if we also ahve 
to define a separate channel for passing the URI.

   Jonathan was proposing something like
> 
> - "" has a property called strict-validation-schema whose value is L.dtd
> - the nature of L.dtd is that it's a DTD

It seems clear to me that independent of the contradiction issue, the 
_whole point_ of RDDL is to define relationships between the namespace 
and its associated files. If you don't use RDF in a way that would do 
that, then you should just use a a proprietary linking strategy or XLink.

> and you get no contradictions.  BUT, you get way more tangled-looking 
> syntax and it gets way harder to predefine a bunch of precooked purpose 
> vocabularies AND it gets harder to automatically detect the "purpose" 
> property.  So this would be an example of the "RDF tax" that has for 
> example doomed the RDF version of RSS.

First, could you please be more concrete about all of these? A syntax 
example would be helpful. I could guess but an RDF-in-XML expert may 
know short-cuts that I don't know. Also, is it harder to detect the 
purpose for an RDF processor or just a general-purpose XML processor 
with RDF knowledge?

Second, this is just further evidence that RDF/XML is broken. On a 
project for a customer it would be appropriate to just hack around it. 
But on a W3C project it seems that the right thing to do is track down 
the people who can fix RDF/XML and get them to do so. If people who WANT 
to use RDF properly feel that they cannot, that is a serious issue.

Finally, a whole 'nother strategy is to define a mapping from an 
optimized XML syntax into the RDF model.

BTW, the 1.2 example is not well-formed:

<rdf:description about="http://example.org/schemas/L.rng
     rddl:title="Relax NG Schema"
     rddl:nature rdf:resource="http://relaxng.org/ns/structure/1.0"
     rddl:purpose rdf:resource="http://www.rddl.org/purposes#validation"
     rddl:prose rdf:resource="#rng-prose" />

  Paul Prescod
Received on Sunday, 10 November 2002 18:32:15 GMT

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