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Is there a way to say, in a DTD things like:

(1) The default value of attribute X is the value of attribute Y?

(2) The default value of attribute X is the value of attribute Y
appended by the text "BLAH"?

(3) The default value of attribute X is "BLAH" if attribute Y has
value "BLING", or "BOING" otherwise?

(4) The default value of attribute X is "BLAH" if attribute Y is
present, or "BOING" otherwise?

Or various other possibilities beyond the simple "the default value is
such-and-such and that's all there is to it"?

If I need such concepts, and it's not possible, obviously I have to do
them at the application level, and pretend at the XML level that
they're just "#IMPLIED". Is that somehow considered an invalid,
incorrect, impure, evil, or otherwise negative thing to do?

Thanks,

Bob Vesterman.

> Is there a way to say, in a DTD things like:
> ...
No

> If I need such concepts, and it's not possible, obviously I have to do
> them at the application level, and pretend at the XML level that
> they're just "#IMPLIED". Is that somehow considered an invalid,
> incorrect, impure, evil, or otherwise negative thing to do?

It's the way life is. It's certainly not invalid, I leave others to
judge harder concepts such as impurity or evil

David

Robert William Vesterman wrote:

> Is there a way to say, in a DTD things like:
>
> (1) The default value of attribute X is the value of attribute Y?

In a *DTD*, yes, but only by hardcoding it

<!ATTLIST foo X (a|b|c) "c" Y (c) "c">

A default token list value must be a literal: it can't be a parameter
entity, so it's not possible to hard-code it.

But I find it hard to imagine a circumstance where you want to do this.
Can you explain more? I think you mean that you want to do this in an
XML document instance.

> (2) The default value of attribute X is the value of attribute Y
> appended by the text "BLAH"?

The same answer.

> (3) The default value of attribute X is "BLAH" if attribute Y has
> value "BLING", or "BOING" otherwise?
>
> (4) The default value of attribute X is "BLAH" if attribute Y is
> present, or "BOING" otherwise?

No. You have to use a Schema if you want this level of validation.

> Or various other possibilities beyond the simple "the default value is
> such-and-such and that's all there is to it"?
>
> If I need such concepts, and it's not possible, obviously I have to do
> them at the application level, and pretend at the XML level that
> they're just "#IMPLIED". Is that somehow considered an invalid,
> incorrect, impure, evil, or otherwise negative thing to do?

No, just that DTDs were designed for TEXT documents, not DATA, so
cross-validation of attribute values was not an issue, as it arises
so rarely in normal text documents.

///Peter
--
"The cat in the box is both a wave and a particle"
-- Terry Pratchett, introducing quantum physics in _The Authentic Cat_