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   Re: Object Hierarchie with XML

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  • From: "Steven R. Newcomb" <srn@techno.com>
  • To: andrewl@microsoft.com
  • Date: Thu, 12 Feb 1998 10:10:44 -0500

[CÚcile Baille-Pierre (cecile.baille-pierre@bull.net):]

> > But how simply implement a class hierarchy, i.e "element E is
> > derived from super-Element S and inherit attributes and properties"?

[Andrew Layman (andrewl@microsoft.com):]

> A type hierarchy would use a vocabulary (schema) designed for that
> purpose.  Such vocabularies are not presently part of XML per se,
> though you can find type-hierarchy concepts discussed in several
> papers, such as those at the W3C RDF site and in a paper that I
> co-authored,
> http://www.w3.org/TR/1998/NOTE-XML-data-0105/Overview.html.

In fact, this capability is already available to XML users, by virtue
of the fact that the derivation of object types from one another is
provided by ISO/IEC 10744:1997 for SGML in general, and this standard
has been amended specifically to allow XML's use of these concepts by
means of an XML-legal PI-based declaration syntax.  There is literally
nothing to prevent the adoption and use of this facility by anyone,
regardless of whether W3C chooses to acknowledge that this
internationally standardized facility exists.  The idea of object type
inheritance is far too useful for XML users to ignore it forever.  As
the ISO 10744 "enabling architectures" facility demonstrates, it is
not necessary to create a special DTD syntax or a special kind of
schema to support hierarchies of element type inheritance.  What is
needed is a way to inherit the semantics and structure of any element
types of any DTDs (schemas), regardless of whether they were intended
to be inherited.  That kind of functionality (among others) is
supported by this facility.

There is a pointer to the relevant standard at http://www.hytime.org.
When you get there, look in the table of contents for Annex A.  A.3
("Architectural Form Definition Requirements [AFDR]") is where the
"enabling architectures" facility is described.

-Steve

--
Steven R. Newcomb, President, TechnoTeacher, Inc.
srn@techno.com  http://www.techno.com  ftp.techno.com

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