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General question: Is there any reason why attributes exist at all?

Robin Cover covers some of the issues here:

http://www.oasis-open.org/cover/elementsAndAttrs.html

This debate is also currently raging on the XML-DEV mailing list. There are proponents for both sides of the debate, which can get quite heated!

If you care to dip in you can look at the thread here:

http://www.lists.ic.ac.uk/hypermail/xml-dev/xml-dev-Nov-1999/0998.html

There are strong arguments on either side - even the 'attributes are required for linking' viewpoint isn't firm, as

<leaf shape="obovate" />

<leaf> <shape>obovate</shape> </leaf>

are semantically identical. It largely depends on which you prefer, and how your schema is defined. The id/idref linking mechanism only works within documents. Its unlikely that this will apply in this context as links will be likely *between* documents - and we'll therefore be using XPointers (which are based on XPath).

Its up to the application to decide whether it looks for a shape attribute or element.

Cheers,

L.