Re: [xml-dev] Multiple Inheritance in XML Schema

[Rick Jelliffe <rjelliffe@allette.com.au>]

Ramkumar Menon wrote:
> Gurus,
>
> Why isn't there a straightforward mechanism for multiple inheritance
> in XML Schemas?
> What are the rationales for that design decision? Is it because it
> adds unnecessary complexity?
> I am sure there are strong reasons for this - am interested in knowing them.
> Ram
>   

One view might be that because of the use of grammars and the various 
grouping mechanisms already gives a very sophisticated multiple 
inheritance: and element could contain  A,B,C declared in one group, 
*AND* X,Y,Z declared in another group. 

However, others might quibble that this is not done as part of the type 
systems, and so at most it is a second-class facility in XSD.

Another group might take the opposite view and say that the use of 
grammars is actually precludes any system of mixins, because grammars 
are based on specifying sequences of continuingly contiguous particles: 
wildcards notwithstanding. (Contrast with Schematron, where a 'pattern' 
fits well as a mixin, without a formal inheritance mechanism.)

Cheers
Rick Jelliffe