Complex attribute defaults?

[Robert William Vesterman]

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.

 

[David Carlisle]

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

 

[Peter Flynn]

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