DTDs newbie question

Im trying to write my first DTD and encounter my first problem...

I defined these elements:

<!ELEMENT value (string | int | struct) >
<!ELEMENT int (#PCDATA) >
<!ELEMENT string (#PCDATA) >
<!ELEMENT struct (member)+ >
<!ELEMENT member (name, value) >
<!ELEMENT name (#PCDATA)>

but now i want to define a element 'registry' which a value struct like 
this:
<registry>
     <value>
         <struct>
         ...
         </struct>
     </value>
</registry>

Do i need a schema for that ?

---
Jean-Charles Bertin
Mipsys
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