Define a Foreign Key with a One-to-One mapping

Hi,

This may be a bit of a simple question but...

How do I define a foreign key in my Torque schema with a one-to-one 
mapping ?  No matter what I do I always seem to end up with a one-to-many 
relationship ?

I've tried adding in multiplicity option but it doesnt seem to have any 
effect:

                <foreign-key foreignTable="styledJourneys">
                        <option key="bidirectional" value="false"/>
                        <option key="multiplicity" value="one-to-one"/> 
                        <reference local="journeySetID" foreign=
"journeySetID"/>
                </foreign-key>

I'm using mySQL 5.1 as my database backend

Thanks for your time

Neil