W3C home > Mailing lists > Public > www-xml-schema-comments@w3.org > July to September 2001

Re: [pointless:Partiles:Structure]: i cannot understand this phrase...

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 07 Jul 2001 15:20:16 +0100
To: "choi jongwon" <jwchoi@digiweb21.com>
Cc: <www-xml-schema-comments@w3.org>
Message-ID: <f5bu20on7mn.fsf@cogsci.ed.ac.uk>
"choi jongwon" <jwchoi@digiweb21.com> writes:

> this question is about pointless of Partiles in Structure spec.
> 
> 3.9.6
>  ...
>  Schema Component Constraint: Particle Valid(Restriction)
>  ...
>  ...
>  <choice> 
>   One of the following must be true: 
>   2.2.1 {particles} is empty "and the particle within which this <choice> appears has {min occurs} of 0. "
>   2.2.2 All of the following must be true: 
>    2.2.2.1 The particle within which this <choice> appears has {max occurs} and {min occurs} of 1.
>    2.2.2.2 One of the following must be true: 
>     2.2.2.2.1 The <choice>'s {particles} has only one member. 
>     2.2.2.2.2 The particle within which this <choice> appears is itself among the {particles} of a <choice>. 
> 
>  in above 2.2.1,
>  i cannot understand why "and the particle within which this <choice> appears has {min occurs} of 0." is appended... 
> "{particles} is empty" is not enough?.. 

Because <choice/> is unsatisfiable.  It's like AND and OR considered
as n-ary functions:

  AND() is true ; including <sequence/> as a required part of a
                  content model does not change what it validates

  OR() is false ; including <choice/> as a required part of a content
                  model ensures that it never validates anything

So for <choice/> to be pointless, it must be optional.

ht
-- 
  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@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/
Received on Saturday, 7 July 2001 10:20:13 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Sunday, 6 December 2009 18:12:51 GMT