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Re: XSchema Spec, Sections 2.0 and 2.1 (Draft 1)

  • From: rbourret@d... (Ron Bourret)
  • To: xml-dev@i...
  • Date: Tue, 9 Jun 1998 12:54:24 +0200

xschema and dtd
Simon St. Laurent wrote:

> PP> Resources (namespaces, characters, entities, etc.) are one thing.
> PP> Constraints are another. I'd like to keep them separate.
> JC>And I would like to keep them together.  A matter of taste.
> Unfortunately, I think it's a lot more than a matter of taste. Making XSchemas 
> perform text substitutions requires a much more complex processing model.

It's also a matter of what our goals are.  My original hopes for XSchema were 
relatively modest -- I wanted a standard way to explore DTDs.  A side-effect was 
that parsers could use the information for validation.  I also had some vague 
hopes for schema reuse and laying a foundation for strong typing.

When John pointed out that you couldn't validate an XML document without 
entities and notations, I had to agree and added both to my DTD.  It simply 
didn't occur to me that such validation would be done outside the parser -- the 
back-and-forth between XML applications and parsers described by John and Paul.  
I just assumed that validating parsers would, in the future, read XSchemas as 
they now read DTDs.

Having now read the multitudinous arguments on each side, I have come to the 
conclusion that entities don't belong in XSchema for two reasons:

1) Requiring that a parser include information (an entity definition) from an 
XSchema document just to get a well-formed document is a bad mistake.  
Evolutionary steps that require you to throw away existing software don't have 
much chance of success.

2) I find the view of XSchema-as-schema far more compelling than XSchema-as-DTD. 
 Although both fit my original goal (DTD exploration), XSchema-as-DTD is a dead 
end, while XSchema-as-schema is a building block for the future.

-- Ron Bourret

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