RE: [XML Schema 1.1] No changes to derive-by-restriction, right? (just a simplification of its description in the specification)

I'm not sure I understand the concern, so perhaps you could clarify.  In 
place of a bunch of rather messy rules, there is now what I will call one 
clean rule.  Stated informally, the rule is:  for a content model R to be 
a restriction of content model B, R must not accept any content that would 
be rejected by B. 

Now, as it turns out, that covers only content models, not some of the 
other things associated with complex types, but I think it's a useful step 
forward.  Certainly it's not the case that there are "no rules".  I would 
have thought that, in applying schemas to UML models, this would be just 
what you want:  if A is a B, then the content model for serializing 
information representing A must be a (not necessarily proper) subset of 
that for B.  Why isn't this just what you want?

Noah

--------------------------------------
Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
--------------------------------------








"Paul Kiel" <paul@xmlhelpline.com>
Sent by: xmlschema-dev-request@w3.org
07/17/2009 12:07 PM
 
        To:     "'Michael Kay'" <mike@saxonica.com>, "'Costello, Roger 
L.'" <costello@mitre.org>, <xmlschema-dev@w3.org>
        cc:     (bcc: Noah Mendelsohn/Cambridge/IBM)
        Subject:        RE: [XML Schema 1.1] No changes to 
derive-by-restriction, right? (just  a simplification of its description 
in the specification)


I applaud the effort to remove the "bugs" from the restriction model.  I
think they really were a hindrance to the use of complextype restriction.
On the flip side, a lack of rules for restriction is unfortunate.  I think
schema is used pretty much exclusively as a bottom up "lego block" tool in
terms of data modeling.  It does well at that.  But a restriction model, 
say
for example managing a logical model and a physical or contextual one, is
not there.  And complextype restriction is the problem.  I have yet to 
have
a client that uses complextype restriction.

http://www.w3.org/2005/05/25-schema/OAGi.html see "What features of XML
Schema 1.0 don't meet your needs?"

A lot of folks try to use UML to XSD conversion for logical/physical
generated models.  Some tools do this ok, but most require you to allow 
the
tool to make some schema design decisions (meaning less control).  It 
would
be nice to have complextype restriction become a better alternative.

Of course maybe I have this all wrong.  Perhaps the lack of rules will 
give
some freedom and lead to some interesting implementations of this 
underused
feature.  I would love to see that happen.

Paul Kiel



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paul@xmlhelpline.com
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-----Original Message-----
From: xmlschema-dev-request@w3.org [mailto:xmlschema-dev-request@w3.org] 
On
Behalf Of Michael Kay
Sent: Wednesday, July 15, 2009 2:30 PM
To: 'Costello, Roger L.'; xmlschema-dev@w3.org
Subject: RE: [XML Schema 1.1] No changes to derive-by-restriction, right?
(just a simplification of its description in the specification)

> 
> Derive-by-restriction behaves the same in 1.1 as in 1.0, right?
> 
> The only change is a simplification of its description in the 
> specification, right?
> 

The 1.0 specification gave detailed rules for what restrictions were
legitimate, and these rules prohibited some restrictions that were 
perfectly
reasonable. The 1.1 specification avoids giving detailed rules, and
therefore avoids these problems.

This rather puts the onus on the implementor to devise their own rules, 
and
of course there's a risk they'll get some corner cases wrong - but that's
better than requiring them to implement bugs enshrined in the spec.

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay

Received on Friday, 17 July 2009 16:27:35 UTC