Why doesn't XML have Bag?

[Lars Marius Garshol]

* Lars Marius Garshol 
|
| It is a limitation of DTDs and was introduced because without this
| operator element content models are easily mapped to finite state
| automatons, but the introduction of the '&' separator makes automaton
| generation much more difficult.

* Paul Janssens
| 
| Please correct me if I am wrong here but isn't that trivial?
| (you may get a BIG automaton, but it's not difficult to generate)

This is correct. However, the number of states required for n elements
is n! with this approach (ie: worse than exponential), which means
that the automaton doesn't just get BIG, for reasonably sized content
models it can get ABSOLUTELY MIND-BOGGLINGLY AWFULLY STUNNINGLY
HUGE. :)

To wit:

[24]> (! 10)
3628800
[25]> (! 30)
265252859812191058636308480000000
 
In other words, this approach doesn't work at all.

| and it's 'easily' visualised by the number of possible shortest
| paths between two opposing points on a hypercube.

I can think of easier ways of visualising it, though possibly not
'easier' ones. :)

--Lars M.


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