Weak DTDs

Peter Murray-Rust peter at ursus.demon.co.uk
Fri Oct 17 15:43:31 BST 1997

Thanks Rick,

At 10:13 17/10/97 +1000, you wrote:
>> From: Peter Murray-Rust <peter at ursus.demon.co.uk>
>> 	(a) the author has to conform to a pre-defined spectrum of ideas (e.g. a
>> tax-return). [This is not required for CML, and any conformance is outside
>> what a DTD can deliver - e.g. value verification.]
>An SGML DTD can deliver value verification by using lexical typing.
>The online version of HyTime '97 has details.  For example you can
>specify POSIX regular expressions for values of attributes or
>simple elements.   You can use the lexical type mechanism with 
>any lexical typing system of your own invention, not just POSIX.
>This extensibility is already there. 

Can this be incorporated into an XML DTD? I don't immediately see how...

>> What I'd like to have is a wildcard #ANY (this has
>> already been suggested) which can be used for content models something like
>> the (currently illegal) XML:
>Why not have 
><!ELEMENT ANY  - -   ANY>
><!ELEMENT MOL  - -   (ANY, ATOMS, BONDS)*>   
>That only costs 1 extra level of tag, and fits into existing SGML & XML.

Thanks - this seems like a smart idea, which can be extended. Of course the
'ANY' element is as about as real as the 'press ANY key' :-)

>If the function of a DTD is to abstract out invariant information from
>a class of documents. If your information is particularly variable and
>unforseeable then you need to use a couple more tags to represent what
>you intend.  

Yes. And I suppose I can do the same thing with attributes.


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