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   RE: [xml-dev] Interesting pair of comments (was Re: [xml-dev] Schema Exp

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If this were only a problem of XSD, I wouldn't be 
as concerned, but the problem as someone else pointed 
out is more fundamental.  The URI mechanism really 
falls apart in the face of identifying dynamic 
systems as resources in the abstract although 
we get away with it using code and error messages 
to soak up the gaps (indirection to the rescue).

At some point, we have to face up to some issues that 
unsettle what Richard Dawkins calls 'middle reality' 
and understand their impact:

1.  Declarative systems are limited when it comes to 
describing dynamic systems.

2.  Namespaces are inadequate to identify dynamic 
systems.  I may crack wise about black holes and 
quantum mechanics, but the opaqueness of URIs makes 
them unsuitable for identifying dynamic systems to 
external observers.  An identifier that has to account 
for change has to be, itself, a resource, given the 
current 'middle reality'.
The effects of using them are almost precisely the 
same as watching a traveler cross an event horizon.
The time is infinite as the traveler approaches and no change 
past the horizon is observable.  Thus other than a 
syntax for disambiguating nodes within an instance, 
they are virtually useless unless one breaks the rules 
of the 'middle reality' of URI opacity.

It is time to realize that names and identifiers 
and locations are not the same, and where we indulge 
in that 'middle reality', we ignore the very real 
problems they create by pretending to solve problems 
they don't touch.   We could think about using URNs 
as non-opaque resources and use URIs only as abstract 
identifiers (in the same way an event boundary has 
area but no volume).  However, then we either have 
to admit a URN is NOT a URI or remove the opaqueness 
restriction on URIs, or dump the notion and admit 
that RDDL, catalogs, etc. aren't a nice to have but 
a must have.


From: Pete Cordell [mailto:petexmldev@tech-know-ware.com]

I'm not sure whether this comes under more digging, or clarification,  but
coming from a data-oriented / protocol background I would like to see a
better story on versioning with some urgency.  I see a number of schemas
that either won't be versionable, or will get very ugly when versioned.
(Extending enumerations is an example of the former, and naively extending
elements is an example of the latter.)


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