XML trade off 1 - DTD vs XML Schema

DuCharme, Robert DuCharmR at moodys.com
Wed Jul 21 18:48:00 BST 1999

>I challenge anyone to translate an XML Schema to a mental
>model without the aid of either paper or machine. 

I'll go with the machine, since I have one on my desk, and it has lots of
software on it capable of reading and manipulating XML documents. 

When XMI came out, I had just been studying up on UML, and I thought "Cool!
I'll print out the DTD so that I can look it over on the subway ride home!"
When I saw how big the XMI DTD was, I decided not to print it out--I prefer
not to spend that much time in the subway. My point is that many XML 1.0
DTDs are too big to form mental models of as well (especially when they use
lots of parameter entities), but they're still useful in serious production
environments, and schema that can't be understood by a visual skimming will
still have a lot going for them. The added machine-readability of schemas
has many system development payoffs, not least of which is that it will be
more extensible than SGML-style declarations--once it's in place, adding new
features to it will be easier than adding them to XML 1.0 DTD syntax.

It's adding up to having all the makings of a religious issue, which is too
bad, because two years from now people will be getting work done using both
styles. Each will be more appropriate for certain kinds of projects. 

Bob DuCharme          www.snee.com/bob           <bob@  
snee.com>  "The elements be kind to thee, and make thy
spirits all of comfort!" Anthony and Cleopatra, III ii

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