how to represent it in dtd ?

Question

I have two element action and guid. guid is a required field when action is add. but when action is del it will not appear in file.

How to represent this in dtd ?

Answer 1

You may be able to express what you're saying in XMLSchema, but I'm fairly certain that it isn't possible in DTDs, unless you make "add" and "del" different types of elements (rather than having them both be action elements).