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Re: XML Schema: At Least One of X Elements Must Appear

• To: "Rick Jelliffe" <ricko@a...>
• Subject: Re: XML Schema: At Least One of X Elements Must Appear
• From: ht@c... (Henry S. Thompson)
• Date: 19 Aug 2002 11:24:30 +0100
• Cc: <xml-dev@l...>
• In-reply-to: <010d01c246e0$0060d5c0$4bc8a8c0@A...>
• References: <3A967FE7B99E134C9FE65E2C136560300DE932@l...><010d01c246e0$0060d5c0$4bc8a8c0@A...>
• User-agent: Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.2(beta13) (Demeter)

You guys are all forgetting your history!  At least one of {a, b, c},
in any order, is expressible in DTD, and therefore _a posteriori_ in
W3C XML Schema:

 <!ELEMENT x ((a,((b,c?)|(c,b?))?)|(b,((a,c?)|(c,a?))?)|(c,((a,b?)|(b,a?))?))>

It's certainly not elegant, and it gets worse as the number of
alternatives goes up, but it's not impossible.

If order doesn't matter, and is therefore constrainable, then it's
much easier:

 <!ELEMENT x ((a,b?,c?)|(b,c?)|c)>

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2002, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@c...
		     URL: http://www.ltg.ed.ac.uk/~ht/
 [mail really from me _always_ has this .sig -- mail without it is forged spam]

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    • From: "CHIUSANO, Joseph" <JCHIUSANO@l...>
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