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   Re: XSD: Proposed Goals, Rev. 2

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  • From: Paul Prescod <papresco@technologist.com>
  • To: "Xml-Dev (E-mail)" <xml-dev@ic.ac.uk>
  • Date: Wed, 27 May 1998 11:09:45 -0400

Simon St.Laurent wrote:
> 3. SDDs shall be capable of representing the normalized element and attribute
> structures defined in XML 1.0 DTDs.

> 3 - Paul Prescod suggested removing it.  I like it because it sets a limited
> task, the 'normalized' DTDs. I think 'capable of' leaves open the possibility
> that SDDs can do more than just this.

Simon likes it because it restrains our task, but I'm not sure it
restrains it enough. I'm not convinced that we want to do everything that
normalized element and attribute structures do. Are we going to agree that
we must support exactly the same set of attribute value types, etc. that
XML does?

Just stating that we are trying to build a simple schema language for
verifying elements and attributes should be enough to restrain us
> 5 - Two private respondents have complained that 'easy' is too vague (as in
> 'easy to create, read, and modify').  To me this means SDD's should be
> editable by a human with a reasonable knowledge of XML structures, but I can
> see where this may bother people.  I like the vagueness, I suppose.  Anyone
> have a clearer idea?

Many of the W3C requirements lists use similar wording. Anything relating
to usability is going to be vague.

> 9 - Should we add some kind of bounds to keep SDDs from redefining document
> instance syntax?

If SDDs are defined as an operation built on top of a parser, then that
isn't a problem. They don't even deal with document instance syntax. They
deal with the abstract tree created (which is why they would be easier to
define if XML's semantics/data model were already explicit). 

But anyhow, the bigger concern is that SDD "extensions" could in some way
invalidate the base SDD syntax. If I make an "extension" that rejects half
of the documents, then the base SDD is too flexible. Is that okay? If I
make an "extension" that makes a particular rule more flexible, then the
base (standardized) SDD will complain about errors my extended SDD does
not. Is that okay?
 Paul Prescod  - http://itrc.uwaterloo.ca/~papresco

Three things to be wary of: A new kid in his prime
A man who knows the answers, and code that runs first time

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