metamodels mapping

Hi,


I'm an intalian student interested in metamodels mapping. I have surfed the web looking for 
something that could clarify my dubts, and I read something about MDR module.


I have read that XMI (or other interchange format) are used to exchange model of any levels (M0, M1, 
M2 and M3).


What I really don't understand is the terminology used in different ways. For example, if I export 
metadata from two different repositories, to XML file conforming to a particular DTD, can I say that the 
DTD is a common metamodel to which both the repositories metamodel are mapped? If then I take the 
document and I don't make the reverse mapping, but I simply put directly the files on a potal, so that I 
can let a navigation between metadata contained in the files, can I say that the DTD represent the 
metamodel of the XML repository in which the file is stored? 


I haven't had answer from a direct reading of articles on web or books, so I have decded to ask directly 
to an expert.


I would be very glad if you could help me, I'm having my degree, and I have choosesm a thesis in 
which my department can't help me, because they don't study this argument.


I hope to hear from you, my best regards.


Natascia Pioveri.