XML-Data: advantages over DTD syntax?

[Paul Madsen]

                                          9:31 AM             29/09/97

Hi, I posted this to comp.text.sgml but didn't get much response (thanks J.R.)
_________

The XML-Data specification from Microsoft
(http://www.sil.org/sgml/xml-data9706223.htm) proposes
that the logic traditionally expressed in the DTD (content models, attribute
lists, entity definitions,
etc.) be expressed using the syntax of XML instances instead. 

For instance, instead of the DTD element declaration 

<!ELEMENT book - - (p+) > 

the XML-Data scheme rule would be something like 

<elementType id="book"> 
     <elt href="#p" occurs="PLUS"/> 
</elementType> 

I'm attracted to the the idea if only because it seems "cool". 

But what does this gain us? What deficiencies with the DTD formalism does it
address? 

Is it the ability to extend object types so that one class of object is a
specialization of another more
general class? 

Do not Architectural forms provide the traditional DTD syntax just that
ability? 

Thanks for any insight. 

Paul 


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