[...]

If I understand correctly, in relaxNG, something like:



start = x

x = element x {
   ( a  & b? & c? & d? & e?) |
   ( a? & b  & c? & d? & e?) |
   ( a? & b? & c  & d? & e?) |
   ( a? & b? & c? & d  & e?) |
   ( a? & b? & c? & d? & e )
 }

a = element a {empty}
b = element b {empty}
c = element c {empty}
d = element d {empty}
e = element e {empty}


does what you want, it validates

<x>
 <a/>
 <b/>
</x>

and invalidates

<x>
 <b/>
 <a/>
 <b/>
</x>



Hmmm...I must confess I didn't really explore the shorthand version of RNG--perhaps I should take a look at it.  That is effectively the same as the longhand way I was doing it, and while it doesn't strike me as particularly elegant, it at least takes up less space.



[...]

usually you can persuade yourself that 1,?,+,* is enough and leave cardinality checking to higher up the chain, but if you really need this, then powers of two come in handy:-)


y = element y { z,z,z16,z2}
z16 = z8,z8
z8  = z4,z4
z4  = z2,z2
z2  = z?,z?
z = element z {empty}

validates
<y><z/><z/></y>

but invalidates instances with less than 1 or more than 20 zs.



LOL, well, it's a bit of a hack, but I suppose that works.  Still, it's nowhere near as clean and readable (and after all, readability is one of the big claims of RNG, from what I've seen) as XSD's minOccurs and maxOccurs.

Thanks for the response, David.  Hoping for more of this kind from others.

Doug Glidden
Software Engineer
The Boeing Company
Douglass.A.Glidden@b...

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