Elements cannot be described more than once in DTD, right ?

Marcus Carr mrc at allette.com.au
Wed Sep 22 09:01:21 BST 1999

Pavel Velikhov wrote:

> > How can I express in DTD that affiliate operations in 'set' and 'get',
> > and that merchant has only the 'signup' ?
> You cannot. This is a fundamental problem with DTDs, you will have to
> declare
> operations as (get|set|signup). XSchema can get around this problem.

I don't think that I'd call this a "fundamental problem" any more than I'd complain about not
being able to translate a (deprecated) SGML content model such as:

(foobar, #PCDATA)

into XML. I can use the XML content model:

(#PCDATA | foobar)*

in absolute comfort, but wary of the fact that I need to do a semantic check to ensure that
I'm conforming to the intention of the original content model. Schemas will provide a tidy way
of rolling the structure and semantic checks together, but the concept is the same.

> It is interesting to find out whether this is a serious problem for you,
> or something that you can get around/tolerate.

I'd be a bit surprised if anyone considered this to be a serious problem and amazed if it was
intolerable. :-) Schemas are interesting and will probably play a big role in times to come,
but I don't believe that they offer anything that can't currently be done by other means.


Marcus Carr                      email:  mrc at allette.com.au
Allette Systems (Australia)      www:    http://www.allette.com.au
"Everything should be made as simple as possible, but not simpler."
       - Einstein

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