Draft charter: Data expression sublanguage?

The draft charter calls for compatibility with both XML data and RDF data. 
One the face of it this requires a common data model and query language 
across XML and RDF. For example, it would have to deal with how XML data 
with embedded RDF/XML should be interpreted. That seems like quite a large 
task to have as a subtask of the WG.

Perhaps this is a smaller problem than it appears?

Perhaps a narrowing of focus of the WG would break the symmetry?

A third option would be to say "yes, that's a non-trivial task but it would 
be worth doing". In that case might it make sense as a WG in its own right? 
One of the suggestions made at the workshop was to not actually standardize 
a rule or rule exchange language just now but to standardize a substantial 
reusable component such as an expression language.

Dave