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From Tim Bray <tb...@textuality.com>
Subject Re: A mathematical vision of XML leads to interesting conclusions
Date Sat, 18 Dec 1999 17:09:39 GMT
At 02:54 PM 12/18/99 +0100, Stefano Mazzocchi wrote:
>Topologically speaking, while SGML is an single infinite
>dimension, XML is an infinite set of infinite dimensions. 

Hmm, I have a math degree and smell no topology.  Both XML and SGML allow
an infinite number of names.  Namespaces provide a way (which would work 
in SGML if anyone cared) to partion that infinite set into any number of 
disjoint subsets, each named by a URI.

Having said that, Stefano may be right about the Kozmick Koolness of
namespaces :)

>While there is a proposed XInclude specification that aims to unify the
>need for inclusion of external things, there is very little concern
>about the application of more general object-oriented design patterns,
>such as inheritance.

Well, we all seem to agree that descriptive markup, as in XML, is a good
thing.  Furthermore, everyone now learns in high school that O-O thinking
is good.  Having said that, I just want to point out that a lot of people
have got into a lot of trouble trying to map the notion of inheritance 
onto the space of markup languages.  To start with, XML tries hard *not*
to be O-O by insisting that you separate your data and logic to the
extent possible.  Secondly, it's not clear whether you want to do
inheritance at the instance or schema level.

A few years ago, the then SGML community made a huge titanic effort and
produced something called "architectural forms" which was said to do 
inheritance (sort of); unfortunately, only 25 people in the world ever 
understood it.

Still, it seems that Stefano is correct in saying that something like
inheritance would probably be very handy.  Proposals welcome. -Tim

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