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- From: Bob Kline <email@example.com>
- To: Rick JELLIFFE <firstname.lastname@example.org>
- Date: Tue, 01 Aug 2000 18:53:22 -0400 (EDT)
On Wed, 2 Aug 2000, Rick JELLIFFE wrote:
> RELAX (and DCD) provide something much better: they allow
> co-occurence constraints. I think these are limited to just element
> names and attributes along the ancestor axis, so that
> stream-processing can be done. Schematron allows constraints from
> any axis, including poking around other documents. Dave Ragget's
> Assertion Grammars started the idea AFAIK.
> I have mentioned this before, and I have harped on about it
> frequently and unattractively on the XML Schema mail-lists at W3C.
> But no-one from the public raised it as a Last Call issue, so it
> seems that people don't want it.
Thanks for the information, Rick. The system I'm working on needs it in
a big way. I had assumed it was not going to be feasible, and we've
been listening to a lot of grumbling from our users that its absence in
the first release of the system was going to be crippling (in a
subsequent release we planned to implement what they wanted using
proprietary extensions to Schema). We also assumed that in the face of
all the complaints about how complicated XML schema already is that
proposing the addition of yet another feature had zero chance of
acceptance. But if RELAX provides what we need -- and it's looking
promising -- we may switch from XML Schema to RELAX, even if the fact
that the latter turns out not to be a subset of the former means there
won't really be a smooth transition available to XML Schema (unless, of
course, W3C changes its mind and includes attribute-sensitive content
models after all).