xml-schema derivation

Hello,
I am an assistant in Computer Engineering Department of  Aegian University
in İzmir/Turkey. In my master degree programme, i am getting metadata
structures lesson and my seasonal research is about developing a metamodel
structure for  metamodel processing.My datamodel is from book

   - Guy Tozer, "*Metadata Management for Information Control Business
   Success*", Artech House Publishers, 1999, London, ISBN 0-89006-280-3.

and i want to make a metamodel for the process of metamodelling described
in

Tannenbaum, Adrienne: Metadata Solutions: Using Metamodels, Repositories,
XML, and Enterprise Portals to Generate Informatio on Demand.
Addison-Wesley, 2001.

 using the data management metamodel in Tozer's book.
I develop a xsd for data management metamodel (DMMM) in Tozer's book and
want to use it for Tannenbaum's process metamodel. Also tannenbaum's
metamodel will be used in lower level metamodel so this is a chain.
While i am developing this issue, i want to use "extend" tag in xml but the
relation is not an "extend" relation.So i wanna use something strange but
also the true solution about this problem.
If i want to use the "Entity" type described in DMMM, i want to describe it
like,

<dmmm:entity description = "Beneficiary" >

Also "Entity" is described as a complextype in DMMM xsd.
The problem is, i cant find anything about this structure and this situation
is not supported instantly. I try to "extend" the "schema" element from w3
abstract schema but its not useful cause "schema" is described as an
element.
If u can give me a hint or explain any solution i will be thankful.
Good afternoon,

Okan Bursa

Aegian Univercity
Computer Enginnering Department