Amy,
 
You do 
not give the definition of your "student" type.
 
Let me 
make a few assumptions:
 
1. 
Your "student" type is sufficiently complex that it is worth doing this as an 
extension, rather than just a separate definition (the easy 
way).
 
2. 
Your "student" already contains an address, and you want to replace this with 
the "grad_address".
 
You 
already have a reply from Jack Lindsey making different 
assumptions.
 
If my 
assumptions are correct, you have a slight problem as an extension cannot 
replace the "address" type with the "grad_address" type. I would create a 
new type and derive both "student" and "grad_student" from this. Let's call the 
abstract type "student_base", with a definition that is the same as student but 
without the address. Then "student" extends this by adding the "address" and 
"grad_student" extends it by adding the "grad_address" and the appropriate 
attributes.
 
Note 
that you can make it impossible to create an element based on the "student_base" 
type directly if you like, but this is not strictly 
necessary.
 
Regards
 
Paul 
Spencer
 
 

  -----Original Message-----
From: Amy Wong 
  [mailto:amy_wanes@y...]
Sent: 31 October 2006 
  19:59
To: xml-dev@l...
Subject: [xml-dev] extend 
  two elements? 

Hi, 

I have an element called 
  "grad_student" which extends "student". Now I want to extend "grad_address" 
  element too since "grad_student" element needs address related info. 
  Unfortunately I cannot merge address info from "grad_address" element into 
  "grad_student" element. I am wondering how I can
extend another element 
  when this element already extends a base element?

regards,

    <xsd:complexType name="grad_student">
          <xsd:complexContent>
             <xsd:extension base="student">
                <xsd:attribute name="name" type="xsd:string" use="required"/>
                <xsd:attribute name="grade" type="xsd:string" use="required"/>
             </xsd:extension>
         
 </xsd:complexContent>
       </xsd:complexType>
       <xsd:element name="grad_student" type="xyz:grad_student"/>
       
          <xsd:complexType name="grad_address">
             <xsd:complexContent>
                <xsd:extension base="address"> 
                   <xsd:attribute name="state" type="xsd:string" use="required"/>
                   <xsd:attribute name="zip_code" type="xsd:string" use="required"/>
                </xsd:extension>
             </xsd:complexContent>
          </xsd:complexType>
       <xsd:element name="grad_address" type="xyz:grad_address"/>

  
  
  Low, Low, Low Rates! Check out Yahoo! Messenger's cheap PC-to-Phone 
  call rates.