Weak DTDs

[Rick Jelliffe]

> 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. 


> 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:
> 
> <!ELEMENT MOL (#ANY,ATOMS,BONDS)*>

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.


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.  


Rick Jelliffe

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