Extra Complexity?

John Cowan cowan at locke.ccil.org
Sat Feb 6 22:51:48 GMT 1999

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 at ccil.org
		e'osai ko sarji la lojban.

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