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Re: XML 1.0 - Element order significance

• From: ht@c... (Henry S. Thompson)
• To: "Rawlings, Matthew BGI UK" <Matthew.Rawlings@b...>
• Date: Mon, 22 Jan 2001 09:09:38 +0000

"Rawlings, Matthew BGI UK" <Matthew.Rawlings@b...> writes:

> Is element sequence order significant in XML 1.0? I can see no clear guide
> from the specification - does omission mean significant or not significant?
> 
> Given the example below is it reasonable if told in advance to attach
> significance, .e.g age order or grade order, to the set of brothers?
> 
> <brothers>
> 	</matthew>
> 	</james>
> 	</luke>
> 	</david>
> </borthers>
> 
> I understand that attribute sequence order is not significant in XML. This
> is clear to me from the specification. 

Without looking at the DTD you can't tell.  Somewhat
counter-intuitively, if the DTD says:

<!ELEMENT brothers (matthew,james,luke,david)>

then you can infer that order is _not_ significant, since the grammar
gives you no choice.

If on the other hand it says:

<!ELEMENT brothers (matthew|james|luke|david)*>

then you can infer that order _may_ be significant.  Unfortunately,
you get the possibility of multiple instances as well.

In SGML (and in XML Schema [1]) you can say

<!ELEMENT brothers (matthew & james & luke & david)>

which again allows you to infer that (since the elements can occur in
any order) that order _may_ be significant.

Hope this helps,

ht

[1] http://www.w3.org/XML/Schema.html
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, 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/

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