I have an XML document which contains a number of classes like this:
<Class name="myNiceClass" xmi.id="MyNiceClass">
    <Stereotype xmi.idref="NiceClass"/>
</Class>
<Class name="myUglyClass" xmi.id="MyUglyClass">
    <Stereotype xmi.idref="UglyClass"/>
</Class>

Also a number of stereotypes, like this :
<Stereotype xmi.id="NiceClass" name="NiceClass">
        </Stereotype>
<Stereotype xmi.id="UglyClass" name="UglyClass">
</Stereotype>

And at last some associations:
<Association>
<Association.connection>
<AssociationEnd name="User" xmi.idref="MyNiceClass"/>
<AssociationEnd name="UserOfClass" xmi.idef="MyUglyClass"/>
</Association.connection>
</Association>

My problem is that I want to look at each association and do different
things dependent of the sterotypes of the classes having the association.
If the associations is between a class with a sterotype NiceClass and UglyClass I want to do some stuff, and if the association is between
a class with a sterotype SmartClass and NiceClass I want to do other stuff.

Does anyone understand what I want to do ?

:D

Is it possible ?

Yes and yes. It's basically a three-table join. The best way to do joins in XSLT is with keys: define a key on the primary-key of the element you want to find, and use the key() function to find it, given the foreign-key in another element.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

Ok. Thanks!
I'll have a look at it another day when my brain is a little bit less tired than right now.