XML DTD's and specifying required attributes

Factual Questions
1

Can you specify that either a certain group of attributes is required or another group is required? For example, let’s start with:

<!ATTLIST myAttribute foo CDATA #REQUIRED
bar CDATA #REQUIRED
>

Now suppose that I have another attribute called baz and I want to convey that either foo and bar are required or baz is required. Can that be expressed in a DTD? If so, what is the syntax?

Thanks,
Rob

2

You can’t do it in a DTD. It would have to be a matter of higher-level validation in your program.

But my suggestion would be to make them two separate tags, one that requires foo and bar, and one that requires baz.