XSD enumeration based on elements

[JamesSmithMz]

Hi,
I'm new in XSD. So I like to enforce the creating of the XML-file.
The XML-Strukture would be linke this:

<types>
<type name="x"/>
<type name="y"/>
<type name="z"/>
</types>
<elements>
<elem type ="x"/>
...
</elements>

In my XSD I've defined theat the type/@name is unique, the primary key
and the foreign key is set to elem@type.

My question is:
* can I / (and how) improve the XML input that only the types at the
element are shown which are defined within the types.

I would like to have an effect like an simple type with enumeration.
But this time my definition of the enumeration is the within the types.

Does somebody have an idea how to define this?

Regards,
Rainer