How to translate RDF grammar to XML schema

Dear all,
 
     I'm working on a tool for authoring vocabulary. I started with
creating a tool for storing RDF schema for each vocabulary. It would be
nice if we can manipulate RDF in dataset like we can do with XML. So the
missing piece is a mapping from RDFS grammar to XML schema. If we can do
this, the rest for authoring process is like filling tables in the
dataset. 
     However, I found it's pretty difficult to do so since XML schema is
not flexible enough (to my experience). I'm wondering whether any of you
who ever experienced this issue. I'll be really grateful if someone
could direct me to some example on this or let me know if it is just
impossible. Thank you very much in advance.
 
Sakda