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Re: extension/restriction/group

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 12 Apr 2001 10:41:03 +0100
To: Forge <forge@neonics.com>
Cc: xmlschema-dev@w3.org
Message-ID: <f5bd7aimp5c.fsf@cogsci.ed.ac.uk>
Forge <forge@neonics.com> writes:

> I have a group or complexType that contains 3 elements in an any tag.
> This means they can have any order.

I presume you mean an <all> tag.

> Now i want to make a new complex type that adds one element to it,
> but its location could be anywhere among the other 3.
> Since the extension mechanism only adds elements to the end,
> is there another way to do this?

Sorry, no.  Just as restriction observes the invariant that any
instance of a restricted type definition is also an instance of its
base, so extension guarantees that any instance of an extended type
contains an instance of its base as a prefix -- i.e. that code written 
to process the base will work on the extended version.

I agree that the current strict enforcement of this wrt <all> is
inconvenient in some cases, and perhaps overly constraining.

  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 Thursday, 12 April 2001 05:41:05 UTC

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