Re: [xml-dev] Who can implement W3C XML Schema ?

All of us who worked on the schema specification understand the difficulty 
of reading the specification.  We are and have been very concerned about 

The language had a very broad range of user requirements, it was designed 
by a large committee, and it emerged as a large language..  I don't think 
most of the competitors meet those use cases.  As a simple example, when 
converting a schema to a DTD, you can preserve attribute default values. 
Relax gains much simplicitly by not trying to solve this problem.  I 
happen to think that the schema design is still too big, and I have my own 
favorite list of things I would have left out or done differently.   Most 
other contributors feel the same, but our lists of potential subsets 
intersect only moderately well.  As Henry Thompson has several times 
pointed out:  we tried hard to find the 80/20 point, and found that one 
person's 20 was another person's 80.   May or may not be completely true, 
but that certainly is a significant issue.  Informal surveys indicate that 
almost all of our features are heavily used.

Anyway, the other problem is that the specification is difficult to read. 
I can assure everyone that we struggled mightily and iterated many times 
to make it more accessible.  It's easy to say "this should be easier to 
read", it's much harder to make it both easier to read and truly rigorous. 
 I would welcome a concrete fragment that shows how to do this.  As 
Jonathan has pointed out, there have been attempts to formalize the 
language.  These are indeed more concise and expose some features as more 
(and others as less) symmetrical than they might otherwise appear.  On the 
other hand, such formal specs have proven to be easier to read only for a 
very small community with mathematical education.  There is a large 
community that can't follow them at all.

I don't want to start a big debate on all of this:  it's been raised and 
discussed many, many times (and it is important).  I mostly wanted to 
point out that it's easy to ask for a simpler presentation, much harder to 
show how to make it both accessible and rigorous.  I assure you that being 
precise and rigorous is exceptionally important in a spec such as this. 
Given the complexity of the language, I think we've at least covered most 
details explicitly.

Noah Mendelsohn                              Voice: 1-617-693-4036
IBM Corporation                                Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
Sent by:
03/21/02 11:24 AM

        cc:     (bcc: Noah Mendelsohn/Cambridge/IBM)
        Subject:        Re: [xml-dev] Who can implement W3C XML Schema ?

In a message dated 21/03/02 15:29:20 GMT Standard Time, writes:

XML Schema Part 1 needs to be rewritten. 

Amen to that. Next time round preferably in English.

The goal of any W3C document should be to communicate effectively. XML 
Schema Part 1 fails on that simple but essential criterion.

Andrew Watt
Co-Author XML Schema Essentials

Received on Thursday, 21 March 2002 13:58:07 UTC