Creating and Managing a Relational Database - FileMaker Pro 13: The Missing Manual - page 239

ing relationships when you finally get back to FileMaker (you'll see why on Avoiding Ambi-
guity ) . In your diagram, you can remove the relationship between Customers and Expenses.
You can also axe the one between Customers and Invoices because Customers can find their
Invoices by way of Jobs. With this revision, the ER diagram now looks like Figure 5-8 .
Figure 5-8. Here's the final ER diagram that you'll use as the roadmap for creating your database.
Notice that every entity is related to at least one other entity in some way. Stray, unrelated entities
are so rare in a real database system that if you see one in your diagram, then you should check to
make sure it belongs in your database. Or did you just forget to draw the relationships it needs?
Now's the time to take one last look over your ER diagram. Keep these points in mind as you
check for errors: