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Re: choice, sequence, all: 'easy' XML Schema question

• To: John Graybeal <graybeal@m...>
• Subject: Re: choice, sequence, all: 'easy' XML Schema question
• From: ht@i... (Henry S. Thompson)
• Date: Fri, 18 Feb 2005 10:36:07 +0000
• Cc: xml-dev@l...
• In-reply-to: <p06020406be3929f8cd23@[134.89.13.14]> (John Graybeal's messageof "Wed, 16 Feb 2005 09:10:39 -0800")
• References: <p06020406be3929f8cd23@[134.89.13.14]>
• User-agent: Gnus/5.1006 (Gnus v5.10.6) XEmacs/21.4 (Security ThroughObscurity, linux)

John Graybeal <graybeal@m...> writes:

> If [W3C XML Schema can't require 1 a, 0 or 1 b, any number of c, in
> any order], can you offer a few words about why things were
> constrained in this way?

One reason was that there was disagreement about precedence -- that
is, does

  ( a & b? & c*)

mean

  a c b c 

is allowed, or only

  a c c b

?

Another (perhaps, with hindsight, misguided) reason was to mitigate
the impact on parser writers.

And finally, there was perhaps a somewhat paternalistic (and therefore
again perhaps misguided) feeling that this is bad markup design - you
shouldn't want to do this.  It makes documents hard to read, and hard
to process.  Allowing something unique (e.g. your 'required_element')
to appear in the midst of a large collection of optional elements is
at best unhelpful.

It also seems likely to arise from a confusion between domain
modelling with document design -- if, as seems likely, order is not
significant (that is, where in the group a child occurs bears no
semantic weight), then good markup design is to choose an order and
require it.

Speaking only for myself,

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

• Follow-Ups:
  • Re: choice, sequence, all: 'easy' XML Schema question
    • From: Ronald Bourret <rpbourret@r...>
  • Re: choice, sequence, all: 'easy' XML Schema question
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  • Transmitting XML between different applications
    • From: Mukul Gandhi <mukul_gandhi@y...>
  • Transmitting XML between different applications
    • From: Mukul Gandhi <mukul_gandhi@y...>

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  • choice, sequence, all: 'easy' XML Schema question
    • From: John Graybeal <graybeal@m...>

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