RE: [xml-dev] A single, all-encompassing data validation language -good

[Michael Kay <mike@saxonica.com>]

> I do not find it difficult to imagine a grammar that can 
> specify these constraints; using the set-notation formalisms 
> common in discussions of automata, it's relatively 
> straightforward (handling the various gregorian exceptions 
> gets increasingly difficult and verbose as one grows more and 
> more precise, but it is not inherently beyond the scope of a 
> grammar ... is it?).

I've no idea what the theoretical limits of what you can do with a grammar
are (I don't even know what the accepted definition of "grammar" is), but I
think I have a feel for the practical limits of when grammar ceases to be
the most convenient way of stating the rules. I see people sometimes doing
things with regular expressions that in my view are well beyond that limit.
Why stretch one technology to its limits when you've crossed into a domain
where other technologies do it better?

Michael Kay