RE: [xml-dev] Best Practice - beyond schema

["Anderson, John" <John@Barbadosoft.com>]

Title: RE: [xml-dev] Best Practice - beyond schema

As I understand it, this is one of the problems with derivation by restriction. Yes, a change to the base type should carry through to the derived types. If I use extension and add an element to the base type definition, my derived types don't need to be touched - they will now require that extra element in any document CM conforming to their type. I don't need to go and explicitly change all schemas which extend this type. Changes DO carry through.

However, with restriction, the entire content has to be copied, then restrictions defined, so if I, for example, add an element to the CM of the base type definition, I need to then go and add that to all my derived type definitions. So changes do NOT carry through - they have to be made explicitly (well, they carry through in the sense that all the derived schemas will have errors, but this doesn't classify as "maintainability" in my book).

Restriction is reuse by copy, not reuse by inheritance.

Maybe I'm wrong about this, and the entire CT definition doesn't have to be duplicated in the restriction, but I've tried to get clarification of this in the past without much success, and the XSD primer and any experts I've heard talk about it say this is the case.

John

PS: TANSTAAFL is too long an acronym to parse. It sounds like the name of a South African province.

-----Original Message-----
From: ht@cogsci.ed.ac.uk [mailto:ht@cogsci.ed.ac.uk]
Sent: 18 June 2002 13:47
To: Anderson, John
Cc: Xml-Dev
Subject: Re: [xml-dev] Best Practice - beyond schema

"Anderson, John" <John@Barbadosoft.com> writes:

> Unfortunately, this mechanism below would not seem to remove mainteneance of
> multiple schemas. If you use restriction, any change to the global type will
> (potentially) require all the redefines also to be modified (or at least,
> checked for consistency).

TANSTAAFL -- the whole _point_ of using derivation is so that changes
to the base carry through to the derived types -- if they make changes
to a changed part, then they have to change too -- how else could it
be?

ht
--
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
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