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Paul, You asked what is the purpose of RDDL? Let me try
to take a stab at answering. Although namespace names
officially are pointers into the land of abstract
resources, most namespace names can be resolved via
standard internet protocols, specifically http. So.
The question is, what is at the end of the http namespace
name rainbow? When it type it into my browser what happens?
A) Nothing / HTTP Error
If this is an HTTP error, then this leaves a niave
person who referenced the link with the feeling that
something is "wrong".
Having a URL that is "broken" is bad practice... even
if it was never intended to fetch something. Thus,
there is a good chance an educated person who is not
part of the XML inner circle will be confused, or worse
think that the namespace name is somehow invalid.
IMHO, regardless of it's intellectual purity, this
is just not an option for me...
B) A Schema
This is nice, however, it's not human readable. Also,
given recent schema competition, this is bound to strike
up too much controversy.
C) An human-readable HTML/TEXT document
This is a nice start. It gives the newbie a "warm fuzzy"
that they can actually start to read about what the
namespace means. This is the best yet, unfortunately,
it is not very usable by computers.
D) A resource directory
This is a very big improvement over (B) since it gives
automated processes a way to find out things about
documents using the namespace. For example, it could
give a RELAX schema, a W3C schema, a Schematron schema,
or all of them without bias. It could also give a
XML -> XHTML XSLT transform. The possibilities here
are limited by your imagination.
E) It can point to a document that is a mix of (C) and (D).
This gives the best of both worlds; HTML for the humans
and a resource for automated processes.
RDDL implements (E) which IMHO, is very novel and clever. These
various solutions bounced around on this list for some time
without resolve till someone (Tim Bray?) proposed E. From
there Jonanthan and others took this "concensus" on the xml-dev
list and made RDDL. After a few rounds of feedback (also on
xml-dev) it is as found at http://www.openhealth.org/RDDL/
Many great people throw other issues into the mix such as
(1) authentication, (2) security, (3) efficency, (4) cashing, etc.
Perhaps I'm just not smart enough, but I've yet to be convinced
that these are not completely othogonal issues. Lastly,
another issue thrown in is that RDDL is controlled by the
namespace owner. I figure if this becomes enough of a problem,
some other mechanism will emerge that is more of a collaborative
mechanism, and probably one that works _with_ RDDL rather than
directly competing with it.
Thus far, I'm impressed with RDDL and the problem it nicely
solves. As YAML grows, YAML will have the same issues to
deal with, and I'm glad I can rest upon the body of knowledge
constructed here at XML-DEV to guide the YAML solution.
Most likely it will be a very similar solution to RDDL.
I hope this helps,
Clark C. Evans Axista, Inc.
XCOLLA Collaborative Project Management Software