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- From: Michael Rossi <mrossi@crusher.jcals.csc.com>
- To: xml-dev@lists.xml.org
- Date: Fri, 27 Oct 2000 13:30:47 -0400
Evan Lenz wrote:
>
> In a DTD, is it possible to not constrain order on a given set of possible
> elements, while still constraining quantity?
>
> For example
>
> <!ELEMENT foo (bar, bat?, bang*)>
>
> Can I somehow allow bar, bat, and bang to be in any order? I suspect not
> but would love to be corrected.
In an SGML DTD you would do this with the "&" operator.
Unfortunately, XML has dropped the "&" in the interest of simplicity (that
is, simplicity of parser implementation). Maybe now that we're all
sophisticated enough to handle XML Schemas, we should bring back the "&" in
DTDs. :-) But I digress.
It might still be theoretically possible to model this in XML DTDs
if you did something more sophisticated like:
<!ELEMENT foo ( (bar, bat?, bang*) | (bat?, bar, bang*) | (bang*, bar, bat?)
... )>
But I SERIOUSLY doubt this could be done unambiguously for all possible
combinations, and as you can see would quickly become far to complex a
solution for all but the simplest content models. Sorry.
Michael A. Rossi
Computer Sciences Corporation
mailto:mrossi@csc.com
856-983-4400 x4911
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