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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:firstname.lastname@example.org]
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.)