To create Reference field in the Drop down box or List Box
following steps are to be followed :
  
1> Open the Property window of Drop down box or List Box.
  
2> Click on "Reference" button which opens up a new window 
having a title "Set References".
  
3> Select a table name from the provided Drop down box.
  
4> On selecting the table name,all the column names of that table
gets listed in the other provided Drop down box.Select the column
name from the listed ones.
  
5> Click on "Save" button to set the reference and save the changes.
  
6> Click on "Exit" button to return back to the OCM user interface.