Define general element

Dear All,

I'm not sure if this is the right place to ask this question but I 
couldn't find a forum or bb on the net better than this.

I'm using xml-files as a long-term persistency for my application. 
Naturally file-size is quite big on average and I don't want to use an 
exact schema because the effort of keeping it up-to-date is just to big.

All my objects (that become xml-elements) DO have something in common 
like:

 ALL elements in the xml-file will have an attribute 'id' and and an 
attribute 'role'
SOME elements do have an attribute 'action'

Is it possible to model these constraints using XML Schema, even if I 
don't wont to create named elements (ie <xs:element name="ObjectA" ...) ??

Your help is very much appreciated!

THX