The challenge demonstrated here are setting the value of both the parent and the child of a cascading LOV.
The problem is that the change of the parent triggers the refresh of the child LOV which sets the values to null.
To set the value of the parent we have a DA that gets the value of the parent and the child from the server.
The value for the child item is stored in a hidden item.
Refreshing the selectlist of the child item triggers the framework events beforerefresh and afterrefresh.
I have used the afterrefresh trigger for a DA to set the value of the child item from the hidden item.