If you are modeling an object which will never change at all (like a Rectangle)
then you would be best to do something like this:
<RECTANGLE x="0" y="0" width="0" height="0"/>
The rationale for this approach over using elements is that in most XML processors
you will get all of the attribute values at once that are necessary for generally
immutable objects like Rectangle's. In a particular application of mine I found
that I would call setBounds() in java.awt.Component 4 times using the element
approach vs. only once with the attributes approach.
If you are representing something whose type may evolve over time like a user
profile in a database, then the element approach I feel works better in the long
run...
Tyler