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Re: DCD v DTD?

• From: rbourret@d... (Ron Bourret)
• To: xml-dev@i...
• Date: Mon, 28 Sep 1998 10:23:21 +0200

> Can someone provide some perspective on the use of DCDs v DTDs?
> 
> This is what I know:
> 1) DTDs are standardized and ready now.

Correct.

> 2) DCDs use XML to describe that which you would use DTDs for (?)

Yes.  (XSchema, too.)

There are a two major advantages to using XML syntax for schema information 
rather than DTDs.  The first is the availability of tools -- while there are 
plenty of tools around for manipulating XML files, there are few available for 
manipulating DTDs.

The second advantage is extensibility.  Because of the stated goal that XML be 
compatible with SGML, XML DTDs are (in theory) extensible only if the same 
extension is simultaneously made to SGML DTDs.  This makes it difficult to add a 
lot of interesting schema information, such as data types, to XML DTDs.  Because 
there is no such requirement when schema information is represented in XML, the 
field is open.

The only drawback (besides short-term availability) is if your application 
requires a DTD.  This is not always the case, as it is often possible to 
separate authoring (which validates against schema information) from use (which 
assumes validity).  And even if your application requires a DTD, you might be 
able to convert part of your schema information into DTD form while still using 
the additional XML-based schema information (such as data types) in your 
authoring tools.

-- Ron Bourret

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