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   Re: Extra Complexity?

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  • From: John Cowan <cowan@locke.ccil.org>
  • To: xml-dev@ic.ac.uk
  • Date: Sat, 6 Feb 1999 18:42:10 -0500 (EST)

Samuel R. Blackburn scripsit:

> It depends on how you use XML. If you use it to transfer
> data between applications then DTD's are completely useless.

Not so.  DTDs make sure that container elements have the appropriate
content, provide default information, and allow access to non-XML
components in a standardized way.  They also permit the representation
of data that is not a tree, and even allow datatype declarations.
Furthermore, they allow limited amounts of data reuse.

> Their assumption that the world is flat is inappropriate for
> data applications.

What do you mean by "flat"?

> Also, the validations performed using DTD's
> don't buy you anything. The application must perform its own
> validation based upon some business rules.

DTD validation is often not sufficient, but that does not mean that it
is not useful.

> DTD's allow you
> to "validate" that a field contains a number but you can't use
> DTD's to "validate" that a field contains a prime number (that
> is an application layer validation).

In fact, XML DTDs do *not* allow you to validate that a "field"
(whether than means an attribute value or #PCDATA content) is

> If you want to replace HTML (i.e. pretty text) then DTD's become
> useful.

They are useful for far more than that.  Documents are complex data,
and simple data can also benefit from what is downright essential
for complex data.

John Cowan					cowan@ccil.org
		e'osai ko sarji la lojban.

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