On 2007-08-06 21:44:32 -0400 Michael Kay <mike@s...> wrote:
> Say you've got a schema that says an element representing data for a 
> month
> must have at most 31 children, and you decide you want to be a bit 
> more
> precise and say it must be 30 for some months and 31 for others and
> occasionally 28 or 29. Does this refinement mean you are doing 
> something of
> a fundamentally different nature? I think not. It does mean that 
> you've
> crossed the limits of what can be done with a grammar-based approach, 
> but

Really?

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?).

It probably does require a pushdown automaton to parse, but it's not 
really beyond the scope of grammar, is it?  Am I being misled by a 
late introduction to formalisms and automata?

I'll grant that it's utterly beyond the capability of W3C XML Schema, 
but ... well, that's not the best definition of grammar around, is it?

In fact, co-occurrence constraints are not, inherently, out of scope 
of grammar, are they?  I recently went to look at what W3C XML Schema 
1.1 is doing, and was ... well, not surprised, perhaps, but at least 
disappointed.  Given the advances in understanding of XML grammars 
since the publication of 1.0, I had hoped to see some interesting 
cleanup.  Instead, the changes seem to be more on the order of adding 
exceptions and special cases, a sort of second system effect for the 
second system ....

Amy!
-- 
Amelia A. Lewis                    amyzing {at} talsever.com
But pain ... seems to me an insufficient reason not to embrace life.
Being dead is quite painless.  Pain, like time, is going to come on
regardless.  Question is, what glorious moments can you win from life
in addition to the pain?
    -- Cordelia Naismith Vorkosigan [Lois McMasters Bujold, "Barrayar"]