From: "Sean McGrath" <>
> I think Rick's thinking (and I agree with it) is that rule based validation
> constraints
> that concentrate on constraining aspects of the structure rather than the
> whole structure, do not "degrade" as extra constraints need to be added
> into the validation.
What he said.
> The theoretical expressibility of constraints in either grammer or rule
> based systems in not the central concern here. The concern is how
> robust the two approaches are in the face of (inevitable) real world
> change.
And Michael is right: we could image a grammar-based system in which the
grammar was open by default and multiple content models could be applied
in parallel to elements (sort-of like James Clark's solution to the <html:a>
inclusion exception problem, where he uses several RELAX NG schemas
in parallel.) That would work (as far as constraining siblings: not a general
solution to marking up arbitrary data structures), but such a beast does
not exist.
Cheers
Rick Jelliffe
