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RE: Inheritance in XML

• To: Mohammad Ghazal <mghazal@v...>
• Subject: RE: Inheritance in XML
• From: "Bullard, Claude L (Len)" <len.bullard@i...>
• Date: Fri, 18 Jun 2004 10:09:45 -0500
• Cc: xml-dev@l...

As Elliotte says, there isn't one.

1.  XML is a syntax specification.  This enables one to 
*design a vocabulary*.  While fun, one is advised not to 
do this unless there isn't an existing one for the task 
at hand or the itch is too bad not to scratch.  See

http://tbray.org/ongoing/When/200x/2004/06/17/CustomSchemas

for discussion.  I agree with Tim's position.  Reuse is better.

2.  The rules for using that vocabulary are specifically 
left to the semantics of the processing application. 
XML doesn't care.

3.  Because XML provides a tree structure, one can use 
the structure to infer has-a relationships and/or names 
(eg, element names) to infer IS-A relationships.  This 
is the responsibility of the application processor or 
as described below, an XML system.

If not as specified, it is convenient to think of XML as

a) XML: the specification for the syntax

b) XML application languages:  a defined XML language 
such as XHTML, SVG, ebXML, X3D and so on.

c) XML systems:  processors that do apply semantics 
to a given application language or languages. 
an XHTML browser is an XML system.  An X3D or SVG 
browser is an XML system.  A SOAP processor is an 
XML system, and so on.

What you would be searching for is examples of application 
languages that do specify inheritance and type/subtype 
relationships such as XML Schema (.xsd) or any of a 
multitude of experiments and working systems that do 
this.

len


From: Elliotte Rusty Harold [mailto:elharo@m...]

At 12:14 AM +0200 6/18/04, Mohammad Ghazal wrote:
>Dear Sir,
>	I would like to know the relation between XML and the
>Inheritance/Subtype concepts, I have read from several books and I
>searched over the internet and I have not found any resources talk about
>this concept, so that I will be thankful to your reply.

It's roughly the same as the relationship between a grapefruit and a 
bicycle. That is, there isn't one. :-)

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