Re: some notes

[Matt Gushee <matt@it.osha.sut.ac.jp>]

Odile Bénassy writes:

 > Ok, I understand what XML is, an extension to HTML, making imaginative
 > customizing possible - is it right ?

Not exactly. When browsers support it, it will be possible to use XML 
to extend the capabilities/services of the web. It can also (already)
be used on the server side for generating dynamic content. These are
indeed the main *uses* being currently contemplated.

But considered as a language, XML is not an extension to HTML at all,
and could be applied to print publishing as well as online
documents. In technical terms, HTML is an 'SGML application' -- an
SGML-based markup language designed for a specific purpose (in this
case, for WWW documents). SGML is a metalanguage -- noone writes
documents in SGML per se; rather, SGML is used to define
special-purpose markup languages (including HTML and many others),
which are then used by authors to create documents.

XML is also a metalanguage. It is a subset of SGML, with, as someone
said in a presentation I attended, '80% of the functionality and 20%
of the hassles of full SGML.' XML syntax is a modified version of SGML
syntax, and it is used in just the same way, to define markup
languages, which are then used by authors or programs to create
documents. Thus, it would be possible to define HTML in XML instead
of full SGML -- and rumor has it that this may in fact happen in the
future.

I hope this doesn't add to the confusion. I just thought I ought to
let you know that there's a lot more to XML than making fancy web
pages.

Regards,
Matt Gushee
Oshamanbe, Hokkaido, Japan