I have successful define a one-to-one mapping when one keyfield is used. for example:
Table address with field adrno
Table addressaddition with field adrno 1:1 to address.adrno

<class name="Address" table="vkunadr">
<id name="AdrNo" access="field.pascalcase-underscore" column="adrno">
<generator class="assigned" />
</id>
<one-to-one cascade="all" name="AddressAddition" class="AddressAddition" access="field.pascalcase-underscore"/>
</class>
</hibernate-mapping>

<class name="AddressAddition" table="vkunzus">
<id name="AdrNo" column="adrno" access="field.pascalcase-underscore">
<generator class="foreign">
<param name="property">Address</param>
</generator>
</id>
<one-to-one name="Address" class="Address" access="field.pascalcase-underscore"/>
</class>

But my problem is to define a one-to-one mapping for 2 fields. Example
Table1, Field f1 + Field f2
Table2, Field f1 + Field f2, 1:1 to the 2 fields of Table1

How can i define this mapping?

I think, that is not possible. Use a many-to-one instead and set the unique attribute:

Thank you very much! This works fine!