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   Re: "XML is a subset of SGML" - True or False?

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  • From: "G. Ken Holman" <gkholman@cranesoftwrights.com>
  • To: xml-dev@xml.org
  • Date: Sun, 02 Jul 2000 14:57:45 -0400

At 00/07/02 08:19 -0400, AndrewWatt2000@aol.com wrote:
>The XML 1.0 Recommendation starts off with a statement to the effect that XML
>is a subset of SGML.
>My question is whether that statement was true at the time it was published
>and whether it is true now.

Yes and yes.

There have been a number of technical corrigenda (TC) published for 
SGML.  With the Web-enabling TC 
http://www.ornl.gov/sgml/wg8/document/1955.htm considered, XML *is* an 
application-profile of SGML.  This TC was published in December 1997 before 
XML 1.0 became a completed Recommendation in February 1998.

>Take for example the optional nature of a DTD in XML. Such a document is
>legal "XML" but is not, as far as I understand it, legal "SGML".

All of XML is legal SGML when considering the appropriate TC applied to the 
SGML standard.  See section K.4.9 that covers this particular aspect.

>Similarly, XML is case sensitive whereas SGML is not.

Not true.  The concrete reference syntax for SGML is not case sensitive, 
but the SGML user can specify in the SGML declaration the feature NAMECASE 
GENERAL NO to stop name case folding to uppercase, thus making it case 

>On these two points alone it seems to me that XML is NOT and NEVER WAS a
>"subset" of SGML, in any strict sense. Am I missing something fundamental
>here or is the opening statement of the XML 1.0 Recommendation inaccurate?

I hope the information above helps.

>The secondary part of my question relates to the implications of XML Schema
>for the assertion that "XML is a subset of SGML". As far as I am aware SGML
>has no such feature. If so, then (yet another) aspect of XML lies outwith the
>SGML domain.

XML Schema is not an aspect of XML 1.0 ... it is a totally separate 
Recommendation.  XML 1.0 is an application profile of SGML.

................. Ken
Chairman Canadian CAC/ISO/IEC JTC 1/SC 34
Document Description and Processing Languages
(SGML family of International Standards)

G. Ken Holman                    mailto:gkholman@CraneSoftwrights.com
Crane Softwrights Ltd.             http://www.CraneSoftwrights.com/x/
Box 266, Kars, Ontario CANADA K0A-2E0   +1(613)489-0999   (Fax:-0995)
Web site: XSL/XML/DSSSL/SGML services, training, libraries, products.
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-                                    2000-10-05,2000-11-13,2001-01-27

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