You can implement your model in SQL*Plus without using any tool. Simply create the table and constraints.
That being said, if I had a FK constraint pointing to only a portion of a composite primary key, I would probably rethink my design. Are you sure that your design is correct and conforms to the Third Normal Form (3NF)? If you are not 3NF, then you run the risk of introducing data anomolies.
This was first published in May 2006