xml-dev - RE: Will XML change the character of W3C?

["Christopher R. Maden" <crism@lexica.net>]

No slight to Karl meant by this correction - he's got a few more years' 
SGML experience than I do.  And if you don't care about SGML, just stop 
reading now.

<sgml-geekitude>
At 08:43 19-10-2000 -0400, Karl Best wrote:
>XML as initially created was supposed to be a true subset of SGML, but such
>things as the optional occurence markers in DTD element declarations,

No - if the SGML declaration had OMITTAG NO, the _omitted tag minimization_ 
was optional (see ISO 8879, production [116]).

>and
>the empty tag syntax, were not SGML-conformant.

Again, no: if you declared net as '/>', then <tag/> parsed as a net-enabled 
start-tag for empty element "tag", which was fine since an empty element 
couldn't have an end-tag.  This was one of the justifications for that 
syntax, since we didn't think we could change SGML at all.

>So, to keep XML as a true
>subset of SGML, SGML had to be tweaked. The W3C XML committee asked the ISO
>SGML committee for some minor changes, and they released a revision (not the
>right word, but I can't remember what it was called; some sort of silent
>change) to the SGML standard in ~1997.

The only real substantive changes are the &#xhhhh; syntax for hex character 
references and predeclared entities (amp, quot, lt, gt), and we were 
prepared to live without those.  Mere well-formedness was also a new 
concept for SGML, but most SGML parsers could already cope with it.

>So, XML is not compliant to ISO 8879-1986 as published in 1986, but it is
>compliant with ISO 8879 as it exists after the ~1997 change. So any SGML
>parser that supports the later version of SGML should also support XML.

James Clark's <URL:http://www.w3.org/TR/NOTE-sgml-xml> contains an SGML 
declaration that lets most valid XML documents parse with a fully-compliant 
SGML system:

<quote>
The following SGML declaration takes advantage of the Extended Naming Rules 
Technical Corrigendum to ISO 8879, but does not make use of the Web SGML 
Adaptations Annex:
</quote>

The ENR facilities are only needed if you're using Unicode, and they're 
necessary whether you're using Unicode with or without XML.

The problem that most legacy SGML systems have is that they don't support 
alternate concrete syntaxes.

</sgml-geekitude>

-Chris
--
Christopher R. Maden, Senior XML Analyst, Lexica LLC
222 Kearny St., Ste. 202, San Francisco, CA 94108-4510
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