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   Re: XML-Data: advantages over DTD syntax?

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  • From: Jonathan Robie <jwrobie@mindspring.com>
  • To: Michael Leventhal <michael@textscience.com>
  • Date: Mon, 29 Sep 1997 11:49:02 -0400

XML-Data adds several features that hard-core object oriented folks

1. True inheritance, with semantics more similar to that of OO
languages than indirect mechanisms used to simulate inheritance when
using architectural forms. Architectural forms do not really give us
what OO folks call inheritance.

2. Reflection - the ability to modify the content model at run-time.

3. The syntax for the content model is the same as the syntax for
data, making it easier to write code to manipulate both.

Of course, all existing SGML and XML tools know how to deal with DTDs,
and this is a rather major departure from traditional SGML. It has not
been blessed by any standardization committee. Given the way Microsoft
has approached Java, insisting that it need not implement the portable
libraries everyone else is using, and encouraging people to use their
platform-specific libraries instead, it is easy to wonder what will
happen to the SGML world if Microsoft is in control of an alternative
method of specifying content models.

According to MS representatives, there *will* be tools to transform
XML-Data content models into DTDs, but still, the "real" content model
is in the XML-Data. Is it worth it in order to gain true inheritance
and reflection? For some applications, it may well be. If Microsoft
controls XML-Data, and some vendors support it but others do not, will
we have the same kind of market fragmentation that we have in the Java
world today, where Microsoft is refusing to support the Java standard
libraries, and instead insists that developers should use their own
libraries, which run only on Windows operating systems?

Who knows!


Jonathan Robie   jwrobie@mindspring.com  http://www.mindspring.com/~jwrobie
POET Software, 3207 Gibson Road, Durham, N.C., 27703    http://www.poet.com

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