I am trying to create a relationship on a database I am working on. Basically I have the following tables:

Table / Key
Customer / CustomerID
Notes/ NoteID
WOrkorder/ WorkorderID

Relationships as follows:

Customer ID one to many NoteID
NoteID many to one CustomerID
Customer ID one to many WorkorderID
NoteID many to one WorkorderID
NoteID many to NONE workorderID

Basically, I need to be able to reference a workorder if there is one relating to the note I enter. However, their may not be a workorder that the note is referencing. How do I set up this optional relationship in Access 2007?