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   Re: XSD and "elements"

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"DuCharme, Bob (LNG-CHO)" <bob.ducharme@lexisnexis.com> writes:

> Henry Thompson wrote:
>>>what is an element declaration declaring
>>the REC never needs to refer to that concept
> Well, I suggest that "manages to avoid" might be more accurate than "never
> needs to." I understand that an XSD schema can have a top level declaration
> for para and two other local ones. In language consistent with XSD
> vocabulary, can we fill in the blank and say that each of these three
> declarations is declaring a ____________? 
> Otherwise, you've got a spec that describes declarations without making it
> clear what they're declaring (element declarations aren't declaring
> elements?), which I find it pretty confusing. 

Fair enough.  My personal memory is that the Working Group never found
anything more concise than e.g. the language in section

  "Element declarations contribute to ·validation· as part of model
  group ·validation·, when their defaults and type components are
  checked against an element information item with a matching name and
  namespace, and by triggering identity-constraint definition

or section 3.3:

  "Element declarations provide for:

    * Local ·validation· of element information item values using a
      type definition;
    * Specifying default or fixed values for an element information items;
    * Establishing uniquenesses and reference constraint relationships
      among the values of related elements and attributes;
    * Controlling the substitutability of elements through the
      mechanism of ·element substitution groups·.

(I note with embarassment that 'element' and 'attribute' have crept in
above as short for 'element information item' and 'attribute
information item' respectively :-(

At various times efforts have been made (see e.g. [1]) to provide a
more formal definition, in which an element declaration is the
characteristic function of an infinite set of (sub-)trees, but my
personal judgement is that none of these efforts, including my own,
have turned out to be very useful.


[1] http://www.w3.org/TR/xmlschema-formal/
 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@inf.ed.ac.uk
                   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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