type-(derivation-)based identity constraints

hello.

one comment for xml schema 1.1: currently, identity constraints are
based on names rather than types (understandably, because they use
xpaths, which do not have a type concept). however, when working with
substitution groups, it would be very nice to have identity contraints
which are based on types (and possibly derived types) rather than names.
i do not know xpath 2.0, maybe it allows type-based xapths (and even
type-derivation-based xpaths). if so, it would be very nice to see this
feature being supported in xml schema 1.1.

cheers,

erik wilde  - tel:+41-1-6325132 - fax:+41-1-6321035
       mailto:net.dret@dret.net -  http://dret.net/
       computer engineering and networks laboratory
       swiss federal institute of technology  (eth)
       * try not. do, or do not. there is no try. *