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Re: My action item on RDDL/RDF

From: Tim Bray <tbray@textuality.com>
Date: Sun, 10 Nov 2002 16:51:45 -0800
Message-ID: <3DCEFF21.5070301@textuality.com>
To: Paul Prescod <paul@prescod.net>
Cc: WWW-Tag <www-tag@w3.org>

Paul Prescod wrote:

> 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 

I'm unconvinced that this really buys anything, but it's probably cheap 
to assert that this RDDL applies to namespace X; obviously you have to 
be able to claim to belong to more than one namespace.  And it's hard to 
see what the harm is as long as the back-pointer isn't compulsory.  So 
in RDF-speak, what's the triple?  What has the property named 
"servesAsRDDLFor" whose value is some namespace name?

>   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.

Well, if you think of a namespace as a resource then a RDDL is a 
representation of that resource, so that establishes one end of the 
relationship.  The RDDL then says that particular other resources have 
properties such as Nature and Purpose, their related-ness is inferred 
from their containment in the representation.  At no point has RDDL ever 
built in syntax to assert the relationship of these resources to the 
namespace, since any reasonable person will point out that this can be 
inferred from its being in the representation of the namespace.

> > 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?

First of all check out one of Jonathan's sketches at 
http://www.rddl.org/RDDL2, which shows off some of his thinking.  If I 
have something like (in N3)

<> <http://www.rddl.org/purposes#schema-validation> <L.dtd>

How do I infer that this is a purpose, especially if you cook up your 
own purposes like

<> <http://prescod.net/purposes#transmogrify> <L.transmog>

Right now, in both the simple XLink and RDF formulations, it's easy to 
use nature/purpose as a two-part key to look up what you want, and 
people seem to like this approach.

> Second, this is just further evidence that RDF/XML is broken.

I increasingly agree.  Every time I try to write something down in 
RDF/XML I get tied in knots; N3 is immensely better.  Either XML is just 
the wrong syntax for RDF, or the design of the current syntax is 
hopelessly hosed. -Tim
Received on Sunday, 10 November 2002 19:51:47 GMT

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