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   Re: Schema concepts

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  • From: Stefan Haustein <haustein@kimo.cs.uni-dortmund.de>
  • To: THOMAS PASSIN <tpassin@idsonline.com>, xml-dev@xml.org
  • Date: Mon, 21 Feb 2000 12:17:27 +0100

> Stefan Haustein wote, responding to my post that responded to Jeff Lowery's:
> > While I agree to your statement, I do not understand the conclusion:
> > Wouldn't a simplified XML Schena spec help all processors, regardless
> > if they are OOP or not?
> >
> Yes, I think simplicity is ***very*** important.  As simple as possible.
> The hard part comes with the addendum: "but as complete as necessary".
> Efforts to be complete tend to sacrifice simplicity, don't they?  In part, I
> imagine, XML-Schema is complex beause the authors are trying to be complete
> about difficult abstractions.  So there are really two issues, aren't there?
> 1) Is the correct set of abstractions present? and 2) if they are, are they
> expressed with as much simplicity as possible?

Yes, that's a good point. So the question arises "what exactly
are the different levels of abstractions covered by <type> and 

(My opinion is that one level of abstraction is enough to 
describe an XML schema. I agree that XML schema 
applications need higher levels of abstractions than just 
the schema syntax, but they cannot be covered inside XML 
schema completely anyway. So, I personally would prefer a
simple schema with a good extension or link-in mechanism 
over the current specs including "some" additional 
abstraction level not fitting my needs.)

> Even if we stuck with an OOP paradigm, there is not universal agreement on
> what either a class or type is.  For example, forget methods, OK, but don't
> we have to leave in inheritance?  But how about multiple inheritance or
> inheritance with restriction (i.e., the child omits some properties of the
> parent)?

BTW: Multiple inheritance is covered neither by <element> nor by <type> 
in the current XML schema specs. 

Best regards


Stefan Haustein
University of Dortmund
Computer Science VIII

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